/*
 *  Driver for Atmel AT91 Serial ports
 *  Copyright (C) 2003 Rick Bronson
 *
 *  Based on drivers/char/serial_sa1100.c, by Deep Blue Solutions Ltd.
 *  Based on drivers/char/serial.c, by Linus Torvalds, Theodore Ts'o.
 *
 *  DMA support added by Chip Coldwell.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */
#include <linux/tty.h>
#include <linux/ioport.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/serial.h>
#include <linux/clk.h>
#include <linux/console.h>
#include <linux/sysrq.h>
#include <linux/tty_flip.h>
#include <linux/platform_device.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/of_gpio.h>
#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/atmel_pdc.h>
#include <linux/uaccess.h>
#include <linux/platform_data/atmel.h>
#include <linux/timer.h>
#include <linux/gpio.h>
#include <linux/gpio/consumer.h>
#include <linux/err.h>
#include <linux/irq.h>
#include <linux/suspend.h>
#include <linux/mm.h>

#include <asm/io.h>
#include <asm/ioctls.h>

#define PDC_BUFFER_SIZE         512
/* Revisit: We should calculate this based on the actual port settings */
#define PDC_RX_TIMEOUT          (3 * 10)                /* 3 bytes */

/* The minium number of data FIFOs should be able to contain */
#define ATMEL_MIN_FIFO_SIZE     8
/*
 * These two offsets are substracted from the RX FIFO size to define the RTS
 * high and low thresholds
 */
#define ATMEL_RTS_HIGH_OFFSET   16
#define ATMEL_RTS_LOW_OFFSET    20

#if defined(CONFIG_SERIAL_ATMEL_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
#define SUPPORT_SYSRQ
#endif

#include <linux/serial_core.h>

#include "serial_mctrl_gpio.h"
#include "atmel_serial.h"

static void atmel_start_rx(struct uart_port *port);
static void atmel_stop_rx(struct uart_port *port);

#ifdef CONFIG_SERIAL_ATMEL_TTYAT

/* Use device name ttyAT, major 204 and minor 154-169.  This is necessary if we
 * should coexist with the 8250 driver, such as if we have an external 16C550
 * UART. */
#define SERIAL_ATMEL_MAJOR      204
#define MINOR_START             154
#define ATMEL_DEVICENAME        "ttyAT"

#else

/* Use device name ttyS, major 4, minor 64-68.  This is the usual serial port
 * name, but it is legally reserved for the 8250 driver. */
#define SERIAL_ATMEL_MAJOR      TTY_MAJOR
#define MINOR_START             64
#define ATMEL_DEVICENAME        "ttyS"

#endif

#define ATMEL_ISR_PASS_LIMIT    256

struct atmel_dma_buffer {
        unsigned char   *buf;
        dma_addr_t      dma_addr;
        unsigned int    dma_size;
        unsigned int    ofs;
};

struct atmel_uart_char {
        u16             status;
        u16             ch;
};

/*
 * Be careful, the real size of the ring buffer is
 * sizeof(atmel_uart_char) * ATMEL_SERIAL_RINGSIZE. It means that ring buffer
 * can contain up to 1024 characters in PIO mode and up to 4096 characters in
 * DMA mode.
 */
#define ATMEL_SERIAL_RINGSIZE 1024

/*
 * at91: 6 USARTs and one DBGU port (SAM9260)
 * samx7: 3 USARTs and 5 UARTs
 */
#define ATMEL_MAX_UART          8

/*
 * We wrap our port structure around the generic uart_port.
 */
struct atmel_uart_port {
        struct uart_port        uart;           /* uart */
        struct clk              *clk;           /* uart clock */
        int                     may_wakeup;     /* cached value of device_may_wakeup for times we need to disable it */
        u32                     backup_imr;     /* IMR saved during suspend */
        int                     break_active;   /* break being received */

        bool                    use_dma_rx;     /* enable DMA receiver */
        bool                    use_pdc_rx;     /* enable PDC receiver */
        short                   pdc_rx_idx;     /* current PDC RX buffer */
        struct atmel_dma_buffer pdc_rx[2];      /* PDC receier */

        bool                    use_dma_tx;     /* enable DMA transmitter */
        bool                    use_pdc_tx;     /* enable PDC transmitter */
        struct atmel_dma_buffer pdc_tx;         /* PDC transmitter */

        spinlock_t                      lock_tx;        /* port lock */
        spinlock_t                      lock_rx;        /* port lock */
        struct dma_chan                 *chan_tx;
        struct dma_chan                 *chan_rx;
        struct dma_async_tx_descriptor  *desc_tx;
        struct dma_async_tx_descriptor  *desc_rx;
        dma_cookie_t                    cookie_tx;
        dma_cookie_t                    cookie_rx;
        struct scatterlist              sg_tx;
        struct scatterlist              sg_rx;
        struct tasklet_struct   tasklet_rx;
        struct tasklet_struct   tasklet_tx;
        atomic_t                tasklet_shutdown;
        unsigned int            irq_status_prev;
        unsigned int            tx_len;

        struct circ_buf         rx_ring;

        struct mctrl_gpios      *gpios;
        unsigned int            tx_done_mask;
        u32                     fifo_size;
        u32                     rts_high;
        u32                     rts_low;
        bool                    ms_irq_enabled;
        u32                     rtor;   /* address of receiver timeout register if it exists */
        bool                    has_frac_baudrate;
        bool                    has_hw_timer;
        struct timer_list       uart_timer;

        bool                    suspended;
        unsigned int            pending;
        unsigned int            pending_status;
        spinlock_t              lock_suspended;

#ifdef CONFIG_PM
        struct {
                u32             cr;
                u32             mr;
                u32             imr;
                u32             brgr;
                u32             rtor;
                u32             ttgr;
                u32             fmr;
                u32             fimr;
        } cache;
#endif

        int (*prepare_rx)(struct uart_port *port);
        int (*prepare_tx)(struct uart_port *port);
        void (*schedule_rx)(struct uart_port *port);
        void (*schedule_tx)(struct uart_port *port);
        void (*release_rx)(struct uart_port *port);
        void (*release_tx)(struct uart_port *port);
};

static struct atmel_uart_port atmel_ports[ATMEL_MAX_UART];
static DECLARE_BITMAP(atmel_ports_in_use, ATMEL_MAX_UART);

#ifdef SUPPORT_SYSRQ
static struct console atmel_console;
#endif

#if defined(CONFIG_OF)
static const struct of_device_id atmel_serial_dt_ids[] = {
        { .compatible = "atmel,at91rm9200-usart" },
        { .compatible = "atmel,at91sam9260-usart" },
        { /* sentinel */ }
};
#endif

static inline struct atmel_uart_port *
to_atmel_uart_port(struct uart_port *uart)
{
        return container_of(uart, struct atmel_uart_port, uart);
}

static inline u32 atmel_uart_readl(struct uart_port *port, u32 reg)
{
        return __raw_readl(port->membase + reg);
}

static inline void atmel_uart_writel(struct uart_port *port, u32 reg, u32 value)
{
        __raw_writel(value, port->membase + reg);
}

static inline u8 atmel_uart_read_char(struct uart_port *port)
{
        return __raw_readb(port->membase + ATMEL_US_RHR);
}

static inline void atmel_uart_write_char(struct uart_port *port, u8 value)
{
        __raw_writeb(value, port->membase + ATMEL_US_THR);
}

#ifdef CONFIG_SERIAL_ATMEL_PDC
static bool atmel_use_pdc_rx(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        return atmel_port->use_pdc_rx;
}

static bool atmel_use_pdc_tx(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        return atmel_port->use_pdc_tx;
}
#else
static bool atmel_use_pdc_rx(struct uart_port *port)
{
        return false;
}

static bool atmel_use_pdc_tx(struct uart_port *port)
{
        return false;
}
#endif

static bool atmel_use_dma_tx(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        return atmel_port->use_dma_tx;
}

static bool atmel_use_dma_rx(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        return atmel_port->use_dma_rx;
}

static bool atmel_use_fifo(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        return atmel_port->fifo_size;
}

static void atmel_tasklet_schedule(struct atmel_uart_port *atmel_port,
                                   struct tasklet_struct *t)
{
        if (!atomic_read(&atmel_port->tasklet_shutdown))
                tasklet_schedule(t);
}

static unsigned int atmel_get_lines_status(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned int status, ret = 0;

        status = atmel_uart_readl(port, ATMEL_US_CSR);

        mctrl_gpio_get(atmel_port->gpios, &ret);

        if (!IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(atmel_port->gpios,
                                                UART_GPIO_CTS))) {
                if (ret & TIOCM_CTS)
                        status &= ~ATMEL_US_CTS;
                else
                        status |= ATMEL_US_CTS;
        }

        if (!IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(atmel_port->gpios,
                                                UART_GPIO_DSR))) {
                if (ret & TIOCM_DSR)
                        status &= ~ATMEL_US_DSR;
                else
                        status |= ATMEL_US_DSR;
        }

        if (!IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(atmel_port->gpios,
                                                UART_GPIO_RI))) {
                if (ret & TIOCM_RI)
                        status &= ~ATMEL_US_RI;
                else
                        status |= ATMEL_US_RI;
        }

        if (!IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(atmel_port->gpios,
                                                UART_GPIO_DCD))) {
                if (ret & TIOCM_CD)
                        status &= ~ATMEL_US_DCD;
                else
                        status |= ATMEL_US_DCD;
        }

        return status;
}

/* Enable or disable the rs485 support */
static int atmel_config_rs485(struct uart_port *port,
                              struct serial_rs485 *rs485conf)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned int mode;

        /* Disable interrupts */
        atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);

        mode = atmel_uart_readl(port, ATMEL_US_MR);

        /* Resetting serial mode to RS232 (0x0) */
        mode &= ~ATMEL_US_USMODE;

        port->rs485 = *rs485conf;

        if (rs485conf->flags & SER_RS485_ENABLED) {
                dev_dbg(port->dev, "Setting UART to RS485\n");
                atmel_port->tx_done_mask = ATMEL_US_TXEMPTY;
                atmel_uart_writel(port, ATMEL_US_TTGR,
                                  rs485conf->delay_rts_after_send);
                mode |= ATMEL_US_USMODE_RS485;
        } else {
                dev_dbg(port->dev, "Setting UART to RS232\n");
                if (atmel_use_pdc_tx(port))
                        atmel_port->tx_done_mask = ATMEL_US_ENDTX |
                                ATMEL_US_TXBUFE;
                else
                        atmel_port->tx_done_mask = ATMEL_US_TXRDY;
        }
        atmel_uart_writel(port, ATMEL_US_MR, mode);

        /* Enable interrupts */
        atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);

        return 0;
}

/*
 * Return TIOCSER_TEMT when transmitter FIFO and Shift register is empty.
 */
static u_int atmel_tx_empty(struct uart_port *port)
{
        return (atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXEMPTY) ?
                TIOCSER_TEMT :
                0;
}

/*
 * Set state of the modem control output lines
 */
static void atmel_set_mctrl(struct uart_port *port, u_int mctrl)
{
        unsigned int control = 0;
        unsigned int mode = atmel_uart_readl(port, ATMEL_US_MR);
        unsigned int rts_paused, rts_ready;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        /* override mode to RS485 if needed, otherwise keep the current mode */
        if (port->rs485.flags & SER_RS485_ENABLED) {
                atmel_uart_writel(port, ATMEL_US_TTGR,
                                  port->rs485.delay_rts_after_send);
                mode &= ~ATMEL_US_USMODE;
                mode |= ATMEL_US_USMODE_RS485;
        }

        /* set the RTS line state according to the mode */
        if ((mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_HWHS) {
                /* force RTS line to high level */
                rts_paused = ATMEL_US_RTSEN;

                /* give the control of the RTS line back to the hardware */
                rts_ready = ATMEL_US_RTSDIS;
        } else {
                /* force RTS line to high level */
                rts_paused = ATMEL_US_RTSDIS;

                /* force RTS line to low level */
                rts_ready = ATMEL_US_RTSEN;
        }

        if (mctrl & TIOCM_RTS)
                control |= rts_ready;
        else
                control |= rts_paused;

        if (mctrl & TIOCM_DTR)
                control |= ATMEL_US_DTREN;
        else
                control |= ATMEL_US_DTRDIS;

        atmel_uart_writel(port, ATMEL_US_CR, control);

        mctrl_gpio_set(atmel_port->gpios, mctrl);

        /* Local loopback mode? */
        mode &= ~ATMEL_US_CHMODE;
        if (mctrl & TIOCM_LOOP)
                mode |= ATMEL_US_CHMODE_LOC_LOOP;
        else
                mode |= ATMEL_US_CHMODE_NORMAL;

        atmel_uart_writel(port, ATMEL_US_MR, mode);
}

/*
 * Get state of the modem control input lines
 */
static u_int atmel_get_mctrl(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned int ret = 0, status;

        status = atmel_uart_readl(port, ATMEL_US_CSR);

        /*
         * The control signals are active low.
         */
        if (!(status & ATMEL_US_DCD))
                ret |= TIOCM_CD;
        if (!(status & ATMEL_US_CTS))
                ret |= TIOCM_CTS;
        if (!(status & ATMEL_US_DSR))
                ret |= TIOCM_DSR;
        if (!(status & ATMEL_US_RI))
                ret |= TIOCM_RI;

        return mctrl_gpio_get(atmel_port->gpios, &ret);
}

/*
 * Stop transmitting.
 */
static void atmel_stop_tx(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (atmel_use_pdc_tx(port)) {
                /* disable PDC transmit */
                atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
        }

        /*
         * Disable the transmitter.
         * This is mandatory when DMA is used, otherwise the DMA buffer
         * is fully transmitted.
         */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);

        /* Disable interrupts */
        atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);

        if ((port->rs485.flags & SER_RS485_ENABLED) &&
            !(port->rs485.flags & SER_RS485_RX_DURING_TX))
                atmel_start_rx(port);
}

/*
 * Start transmitting.
 */
static void atmel_start_tx(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (atmel_use_pdc_tx(port) && (atmel_uart_readl(port, ATMEL_PDC_PTSR)
                                       & ATMEL_PDC_TXTEN))
                /* The transmitter is already running.  Yes, we
                   really need this.*/
                return;

        if (atmel_use_pdc_tx(port) || atmel_use_dma_tx(port))
                if ((port->rs485.flags & SER_RS485_ENABLED) &&
                    !(port->rs485.flags & SER_RS485_RX_DURING_TX))
                        atmel_stop_rx(port);

        if (atmel_use_pdc_tx(port))
                /* re-enable PDC transmit */
                atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTEN);

        /* Enable interrupts */
        atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);

        /* re-enable the transmitter */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
}

/*
 * start receiving - port is in process of being opened.
 */
static void atmel_start_rx(struct uart_port *port)
{
        /* reset status and receiver */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA);

        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RXEN);

        if (atmel_use_pdc_rx(port)) {
                /* enable PDC controller */
                atmel_uart_writel(port, ATMEL_US_IER,
                                  ATMEL_US_ENDRX | ATMEL_US_TIMEOUT |
                                  port->read_status_mask);
                atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_RXTEN);
        } else {
                atmel_uart_writel(port, ATMEL_US_IER, ATMEL_US_RXRDY);
        }
}

/*
 * Stop receiving - port is in process of being closed.
 */
static void atmel_stop_rx(struct uart_port *port)
{
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RXDIS);

        if (atmel_use_pdc_rx(port)) {
                /* disable PDC receive */
                atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_RXTDIS);
                atmel_uart_writel(port, ATMEL_US_IDR,
                                  ATMEL_US_ENDRX | ATMEL_US_TIMEOUT |
                                  port->read_status_mask);
        } else {
                atmel_uart_writel(port, ATMEL_US_IDR, ATMEL_US_RXRDY);
        }
}

/*
 * Enable modem status interrupts
 */
static void atmel_enable_ms(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        uint32_t ier = 0;

        /*
         * Interrupt should not be enabled twice
         */
        if (atmel_port->ms_irq_enabled)
                return;

        atmel_port->ms_irq_enabled = true;

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS))
                ier |= ATMEL_US_CTSIC;

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_DSR))
                ier |= ATMEL_US_DSRIC;

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_RI))
                ier |= ATMEL_US_RIIC;

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_DCD))
                ier |= ATMEL_US_DCDIC;

        atmel_uart_writel(port, ATMEL_US_IER, ier);

        mctrl_gpio_enable_ms(atmel_port->gpios);
}

/*
 * Disable modem status interrupts
 */
static void atmel_disable_ms(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        uint32_t idr = 0;

        /*
         * Interrupt should not be disabled twice
         */
        if (!atmel_port->ms_irq_enabled)
                return;

        atmel_port->ms_irq_enabled = false;

        mctrl_gpio_disable_ms(atmel_port->gpios);

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS))
                idr |= ATMEL_US_CTSIC;

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_DSR))
                idr |= ATMEL_US_DSRIC;

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_RI))
                idr |= ATMEL_US_RIIC;

        if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_DCD))
                idr |= ATMEL_US_DCDIC;

        atmel_uart_writel(port, ATMEL_US_IDR, idr);
}

/*
 * Control the transmission of a break signal
 */
static void atmel_break_ctl(struct uart_port *port, int break_state)
{
        if (break_state != 0)
                /* start break */
                atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_STTBRK);
        else
                /* stop break */
                atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_STPBRK);
}

/*
 * Stores the incoming character in the ring buffer
 */
static void
atmel_buffer_rx_char(struct uart_port *port, unsigned int status,
                     unsigned int ch)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct circ_buf *ring = &atmel_port->rx_ring;
        struct atmel_uart_char *c;

        if (!CIRC_SPACE(ring->head, ring->tail, ATMEL_SERIAL_RINGSIZE))
                /* Buffer overflow, ignore char */
                return;

        c = &((struct atmel_uart_char *)ring->buf)[ring->head];
        c->status       = status;
        c->ch           = ch;

        /* Make sure the character is stored before we update head. */
        smp_wmb();

        ring->head = (ring->head + 1) & (ATMEL_SERIAL_RINGSIZE - 1);
}

/*
 * Deal with parity, framing and overrun errors.
 */
static void atmel_pdc_rxerr(struct uart_port *port, unsigned int status)
{
        /* clear error */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA);

        if (status & ATMEL_US_RXBRK) {
                /* ignore side-effect */
                status &= ~(ATMEL_US_PARE | ATMEL_US_FRAME);
                port->icount.brk++;
        }
        if (status & ATMEL_US_PARE)
                port->icount.parity++;
        if (status & ATMEL_US_FRAME)
                port->icount.frame++;
        if (status & ATMEL_US_OVRE)
                port->icount.overrun++;
}

/*
 * Characters received (called from interrupt handler)
 */
static void atmel_rx_chars(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned int status, ch;

        status = atmel_uart_readl(port, ATMEL_US_CSR);
        while (status & ATMEL_US_RXRDY) {
                ch = atmel_uart_read_char(port);

                /*
                 * note that the error handling code is
                 * out of the main execution path
                 */
                if (unlikely(status & (ATMEL_US_PARE | ATMEL_US_FRAME
                                       | ATMEL_US_OVRE | ATMEL_US_RXBRK)
                             || atmel_port->break_active)) {

                        /* clear error */
                        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA);

                        if (status & ATMEL_US_RXBRK
                            && !atmel_port->break_active) {
                                atmel_port->break_active = 1;
                                atmel_uart_writel(port, ATMEL_US_IER,
                                                  ATMEL_US_RXBRK);
                        } else {
                                /*
                                 * This is either the end-of-break
                                 * condition or we've received at
                                 * least one character without RXBRK
                                 * being set. In both cases, the next
                                 * RXBRK will indicate start-of-break.
                                 */
                                atmel_uart_writel(port, ATMEL_US_IDR,
                                                  ATMEL_US_RXBRK);
                                status &= ~ATMEL_US_RXBRK;
                                atmel_port->break_active = 0;
                        }
                }

                atmel_buffer_rx_char(port, status, ch);
                status = atmel_uart_readl(port, ATMEL_US_CSR);
        }

        atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_rx);
}

/*
 * Transmit characters (called from tasklet with TXRDY interrupt
 * disabled)
 */
static void atmel_tx_chars(struct uart_port *port)
{
        struct circ_buf *xmit = &port->state->xmit;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (port->x_char &&
            (atmel_uart_readl(port, ATMEL_US_CSR) & atmel_port->tx_done_mask)) {
                atmel_uart_write_char(port, port->x_char);
                port->icount.tx++;
                port->x_char = 0;
        }
        if (uart_circ_empty(xmit) || uart_tx_stopped(port))
                return;

        while (atmel_uart_readl(port, ATMEL_US_CSR) &
               atmel_port->tx_done_mask) {
                atmel_uart_write_char(port, xmit->buf[xmit->tail]);
                xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
                port->icount.tx++;
                if (uart_circ_empty(xmit))
                        break;
        }

        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(port);

        if (!uart_circ_empty(xmit))
                /* Enable interrupts */
                atmel_uart_writel(port, ATMEL_US_IER,
                                  atmel_port->tx_done_mask);
}

static void atmel_complete_tx_dma(void *arg)
{
        struct atmel_uart_port *atmel_port = arg;
        struct uart_port *port = &atmel_port->uart;
        struct circ_buf *xmit = &port->state->xmit;
        struct dma_chan *chan = atmel_port->chan_tx;
        unsigned long flags;

        spin_lock_irqsave(&port->lock, flags);

        if (chan)
                dmaengine_terminate_all(chan);
        xmit->tail += atmel_port->tx_len;
        xmit->tail &= UART_XMIT_SIZE - 1;

        port->icount.tx += atmel_port->tx_len;

        spin_lock_irq(&atmel_port->lock_tx);
        async_tx_ack(atmel_port->desc_tx);
        atmel_port->cookie_tx = -EINVAL;
        atmel_port->desc_tx = NULL;
        spin_unlock_irq(&atmel_port->lock_tx);

        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(port);

        /*
         * xmit is a circular buffer so, if we have just send data from
         * xmit->tail to the end of xmit->buf, now we have to transmit the
         * remaining data from the beginning of xmit->buf to xmit->head.
         */
        if (!uart_circ_empty(xmit))
                atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx);
        else if ((port->rs485.flags & SER_RS485_ENABLED) &&
                 !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
                /* DMA done, stop TX, start RX for RS485 */
                atmel_start_rx(port);
        }

        spin_unlock_irqrestore(&port->lock, flags);
}

static void atmel_release_tx_dma(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct dma_chan *chan = atmel_port->chan_tx;

        if (chan) {
                dmaengine_terminate_all(chan);
                dma_release_channel(chan);
                dma_unmap_sg(port->dev, &atmel_port->sg_tx, 1,
                                DMA_TO_DEVICE);
        }

        atmel_port->desc_tx = NULL;
        atmel_port->chan_tx = NULL;
        atmel_port->cookie_tx = -EINVAL;
}

/*
 * Called from tasklet with TXRDY interrupt is disabled.
 */
static void atmel_tx_dma(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct circ_buf *xmit = &port->state->xmit;
        struct dma_chan *chan = atmel_port->chan_tx;
        struct dma_async_tx_descriptor *desc;
        struct scatterlist sgl[2], *sg, *sg_tx = &atmel_port->sg_tx;
        unsigned int tx_len, part1_len, part2_len, sg_len;
        dma_addr_t phys_addr;

        /* Make sure we have an idle channel */
        if (atmel_port->desc_tx != NULL)
                return;

        if (!uart_circ_empty(xmit) && !uart_tx_stopped(port)) {
                /*
                 * DMA is idle now.
                 * Port xmit buffer is already mapped,
                 * and it is one page... Just adjust
                 * offsets and lengths. Since it is a circular buffer,
                 * we have to transmit till the end, and then the rest.
                 * Take the port lock to get a
                 * consistent xmit buffer state.
                 */
                tx_len = CIRC_CNT_TO_END(xmit->head,
                                         xmit->tail,
                                         UART_XMIT_SIZE);

                if (atmel_port->fifo_size) {
                        /* multi data mode */
                        part1_len = (tx_len & ~0x3); /* DWORD access */
                        part2_len = (tx_len & 0x3); /* BYTE access */
                } else {
                        /* single data (legacy) mode */
                        part1_len = 0;
                        part2_len = tx_len; /* BYTE access only */
                }

                sg_init_table(sgl, 2);
                sg_len = 0;
                phys_addr = sg_dma_address(sg_tx) + xmit->tail;
                if (part1_len) {
                        sg = &sgl[sg_len++];
                        sg_dma_address(sg) = phys_addr;
                        sg_dma_len(sg) = part1_len;

                        phys_addr += part1_len;
                }

                if (part2_len) {
                        sg = &sgl[sg_len++];
                        sg_dma_address(sg) = phys_addr;
                        sg_dma_len(sg) = part2_len;
                }

                /*
                 * save tx_len so atmel_complete_tx_dma() will increase
                 * xmit->tail correctly
                 */
                atmel_port->tx_len = tx_len;

                desc = dmaengine_prep_slave_sg(chan,
                                               sgl,
                                               sg_len,
                                               DMA_MEM_TO_DEV,
                                               DMA_PREP_INTERRUPT |
                                               DMA_CTRL_ACK);
                if (!desc) {
                        dev_err(port->dev, "Failed to send via dma!\n");
                        return;
                }

                dma_sync_sg_for_device(port->dev, sg_tx, 1, DMA_TO_DEVICE);

                atmel_port->desc_tx = desc;
                desc->callback = atmel_complete_tx_dma;
                desc->callback_param = atmel_port;
                atmel_port->cookie_tx = dmaengine_submit(desc);
        }

        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(port);
}

static int atmel_prepare_tx_dma(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        dma_cap_mask_t          mask;
        struct dma_slave_config config;
        int ret, nent;

        dma_cap_zero(mask);
        dma_cap_set(DMA_SLAVE, mask);

        atmel_port->chan_tx = dma_request_slave_channel(port->dev, "tx");
        if (atmel_port->chan_tx == NULL)
                goto chan_err;
        dev_info(port->dev, "using %s for tx DMA transfers\n",
                dma_chan_name(atmel_port->chan_tx));

        spin_lock_init(&atmel_port->lock_tx);
        sg_init_table(&atmel_port->sg_tx, 1);
        /* UART circular tx buffer is an aligned page. */
        BUG_ON(!PAGE_ALIGNED(port->state->xmit.buf));
        sg_set_page(&atmel_port->sg_tx,
                        virt_to_page(port->state->xmit.buf),
                        UART_XMIT_SIZE,
                        offset_in_page(port->state->xmit.buf));
        nent = dma_map_sg(port->dev,
                                &atmel_port->sg_tx,
                                1,
                                DMA_TO_DEVICE);

        if (!nent) {
                dev_dbg(port->dev, "need to release resource of dma\n");
                goto chan_err;
        } else {
                dev_dbg(port->dev, "%s: mapped %d@%p to %pad\n", __func__,
                        sg_dma_len(&atmel_port->sg_tx),
                        port->state->xmit.buf,
                        &sg_dma_address(&atmel_port->sg_tx));
        }

        /* Configure the slave DMA */
        memset(&config, 0, sizeof(config));
        config.direction = DMA_MEM_TO_DEV;
        config.dst_addr_width = (atmel_port->fifo_size) ?
                                DMA_SLAVE_BUSWIDTH_4_BYTES :
                                DMA_SLAVE_BUSWIDTH_1_BYTE;
        config.dst_addr = port->mapbase + ATMEL_US_THR;
        config.dst_maxburst = 1;

        ret = dmaengine_slave_config(atmel_port->chan_tx,
                                     &config);
        if (ret) {
                dev_err(port->dev, "DMA tx slave configuration failed\n");
                goto chan_err;
        }

        return 0;

chan_err:
        dev_err(port->dev, "TX channel not available, switch to pio\n");
        atmel_port->use_dma_tx = 0;
        if (atmel_port->chan_tx)
                atmel_release_tx_dma(port);
        return -EINVAL;
}

static void atmel_complete_rx_dma(void *arg)
{
        struct uart_port *port = arg;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_rx);
}

static void atmel_release_rx_dma(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct dma_chan *chan = atmel_port->chan_rx;

        if (chan) {

                dmaengine_terminate_all(chan);
                dma_release_channel(chan);
                dma_unmap_sg(port->dev, &atmel_port->sg_rx, 1,
                                DMA_FROM_DEVICE);
        }

        atmel_port->desc_rx = NULL;
        atmel_port->chan_rx = NULL;
        atmel_port->cookie_rx = -EINVAL;
}

static void atmel_rx_from_dma(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct tty_port *tport = &port->state->port;
        struct circ_buf *ring = &atmel_port->rx_ring;
        struct dma_chan *chan = atmel_port->chan_rx;
        struct dma_tx_state state;
        enum dma_status dmastat;
        size_t count;


        /* Reset the UART timeout early so that we don't miss one */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_STTTO);
        dmastat = dmaengine_tx_status(chan,
                                atmel_port->cookie_rx,
                                &state);
        /* Restart a new tasklet if DMA status is error */
        if (dmastat == DMA_ERROR) {
                dev_dbg(port->dev, "Get residue error, restart tasklet\n");
                atmel_uart_writel(port, ATMEL_US_IER, ATMEL_US_TIMEOUT);
                atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_rx);
                return;
        }

        /* CPU claims ownership of RX DMA buffer */
        dma_sync_sg_for_cpu(port->dev,
                            &atmel_port->sg_rx,
                            1,
                            DMA_FROM_DEVICE);

        /*
         * ring->head points to the end of data already written by the DMA.
         * ring->tail points to the beginning of data to be read by the
         * framework.
         * The current transfer size should not be larger than the dma buffer
         * length.
         */
        ring->head = sg_dma_len(&atmel_port->sg_rx) - state.residue;
        BUG_ON(ring->head > sg_dma_len(&atmel_port->sg_rx));
        /*
         * At this point ring->head may point to the first byte right after the
         * last byte of the dma buffer:
         * 0 <= ring->head <= sg_dma_len(&atmel_port->sg_rx)
         *
         * However ring->tail must always points inside the dma buffer:
         * 0 <= ring->tail <= sg_dma_len(&atmel_port->sg_rx) - 1
         *
         * Since we use a ring buffer, we have to handle the case
         * where head is lower than tail. In such a case, we first read from
         * tail to the end of the buffer then reset tail.
         */
        if (ring->head < ring->tail) {
                count = sg_dma_len(&atmel_port->sg_rx) - ring->tail;

                tty_insert_flip_string(tport, ring->buf + ring->tail, count);
                ring->tail = 0;
                port->icount.rx += count;
        }

        /* Finally we read data from tail to head */
        if (ring->tail < ring->head) {
                count = ring->head - ring->tail;

                tty_insert_flip_string(tport, ring->buf + ring->tail, count);
                /* Wrap ring->head if needed */
                if (ring->head >= sg_dma_len(&atmel_port->sg_rx))
                        ring->head = 0;
                ring->tail = ring->head;
                port->icount.rx += count;
        }

        /* USART retreives ownership of RX DMA buffer */
        dma_sync_sg_for_device(port->dev,
                               &atmel_port->sg_rx,
                               1,
                               DMA_FROM_DEVICE);

        /*
         * Drop the lock here since it might end up calling
         * uart_start(), which takes the lock.
         */
        spin_unlock(&port->lock);
        tty_flip_buffer_push(tport);
        spin_lock(&port->lock);

        atmel_uart_writel(port, ATMEL_US_IER, ATMEL_US_TIMEOUT);
}

static int atmel_prepare_rx_dma(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct dma_async_tx_descriptor *desc;
        dma_cap_mask_t          mask;
        struct dma_slave_config config;
        struct circ_buf         *ring;
        int ret, nent;

        ring = &atmel_port->rx_ring;

        dma_cap_zero(mask);
        dma_cap_set(DMA_CYCLIC, mask);

        atmel_port->chan_rx = dma_request_slave_channel(port->dev, "rx");
        if (atmel_port->chan_rx == NULL)
                goto chan_err;
        dev_info(port->dev, "using %s for rx DMA transfers\n",
                dma_chan_name(atmel_port->chan_rx));

        spin_lock_init(&atmel_port->lock_rx);
        sg_init_table(&atmel_port->sg_rx, 1);
        /* UART circular rx buffer is an aligned page. */
        BUG_ON(!PAGE_ALIGNED(ring->buf));
        sg_set_page(&atmel_port->sg_rx,
                    virt_to_page(ring->buf),
                    sizeof(struct atmel_uart_char) * ATMEL_SERIAL_RINGSIZE,
                    offset_in_page(ring->buf));
        nent = dma_map_sg(port->dev,
                          &atmel_port->sg_rx,
                          1,
                          DMA_FROM_DEVICE);

        if (!nent) {
                dev_dbg(port->dev, "need to release resource of dma\n");
                goto chan_err;
        } else {
                dev_dbg(port->dev, "%s: mapped %d@%p to %pad\n", __func__,
                        sg_dma_len(&atmel_port->sg_rx),
                        ring->buf,
                        &sg_dma_address(&atmel_port->sg_rx));
        }

        /* Configure the slave DMA */
        memset(&config, 0, sizeof(config));
        config.direction = DMA_DEV_TO_MEM;
        config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
        config.src_addr = port->mapbase + ATMEL_US_RHR;
        config.src_maxburst = 1;

        ret = dmaengine_slave_config(atmel_port->chan_rx,
                                     &config);
        if (ret) {
                dev_err(port->dev, "DMA rx slave configuration failed\n");
                goto chan_err;
        }
        /*
         * Prepare a cyclic dma transfer, assign 2 descriptors,
         * each one is half ring buffer size
         */
        desc = dmaengine_prep_dma_cyclic(atmel_port->chan_rx,
                                         sg_dma_address(&atmel_port->sg_rx),
                                         sg_dma_len(&atmel_port->sg_rx),
                                         sg_dma_len(&atmel_port->sg_rx)/2,
                                         DMA_DEV_TO_MEM,
                                         DMA_PREP_INTERRUPT);
        desc->callback = atmel_complete_rx_dma;
        desc->callback_param = port;
        atmel_port->desc_rx = desc;
        atmel_port->cookie_rx = dmaengine_submit(desc);

        return 0;

chan_err:
        dev_err(port->dev, "RX channel not available, switch to pio\n");
        atmel_port->use_dma_rx = 0;
        if (atmel_port->chan_rx)
                atmel_release_rx_dma(port);
        return -EINVAL;
}

static void atmel_uart_timer_callback(unsigned long data)
{
        struct uart_port *port = (void *)data;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (!atomic_read(&atmel_port->tasklet_shutdown)) {
                tasklet_schedule(&atmel_port->tasklet_rx);
                mod_timer(&atmel_port->uart_timer,
                          jiffies + uart_poll_timeout(port));
        }
}

/*
 * receive interrupt handler.
 */
static void
atmel_handle_receive(struct uart_port *port, unsigned int pending)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (atmel_use_pdc_rx(port)) {
                /*
                 * PDC receive. Just schedule the tasklet and let it
                 * figure out the details.
                 *
                 * TODO: We're not handling error flags correctly at
                 * the moment.
                 */
                if (pending & (ATMEL_US_ENDRX | ATMEL_US_TIMEOUT)) {
                        atmel_uart_writel(port, ATMEL_US_IDR,
                                          (ATMEL_US_ENDRX | ATMEL_US_TIMEOUT));
                        atmel_tasklet_schedule(atmel_port,
                                               &atmel_port->tasklet_rx);
                }

                if (pending & (ATMEL_US_RXBRK | ATMEL_US_OVRE |
                                ATMEL_US_FRAME | ATMEL_US_PARE))
                        atmel_pdc_rxerr(port, pending);
        }

        if (atmel_use_dma_rx(port)) {
                if (pending & ATMEL_US_TIMEOUT) {
                        atmel_uart_writel(port, ATMEL_US_IDR,
                                          ATMEL_US_TIMEOUT);
                        atmel_tasklet_schedule(atmel_port,
                                               &atmel_port->tasklet_rx);
                }
        }

        /* Interrupt receive */
        if (pending & ATMEL_US_RXRDY)
                atmel_rx_chars(port);
        else if (pending & ATMEL_US_RXBRK) {
                /*
                 * End of break detected. If it came along with a
                 * character, atmel_rx_chars will handle it.
                 */
                atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA);
                atmel_uart_writel(port, ATMEL_US_IDR, ATMEL_US_RXBRK);
                atmel_port->break_active = 0;
        }
}

/*
 * transmit interrupt handler. (Transmit is IRQF_NODELAY safe)
 */
static void
atmel_handle_transmit(struct uart_port *port, unsigned int pending)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (pending & atmel_port->tx_done_mask) {
                /* Either PDC or interrupt transmission */
                atmel_uart_writel(port, ATMEL_US_IDR,
                                  atmel_port->tx_done_mask);
                atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx);
        }
}

/*
 * status flags interrupt handler.
 */
static void
atmel_handle_status(struct uart_port *port, unsigned int pending,
                    unsigned int status)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned int status_change;

        if (pending & (ATMEL_US_RIIC | ATMEL_US_DSRIC | ATMEL_US_DCDIC
                                | ATMEL_US_CTSIC)) {
                status_change = status ^ atmel_port->irq_status_prev;
                atmel_port->irq_status_prev = status;

                if (status_change & (ATMEL_US_RI | ATMEL_US_DSR
                                        | ATMEL_US_DCD | ATMEL_US_CTS)) {
                        /* TODO: All reads to CSR will clear these interrupts! */
                        if (status_change & ATMEL_US_RI)
                                port->icount.rng++;
                        if (status_change & ATMEL_US_DSR)
                                port->icount.dsr++;
                        if (status_change & ATMEL_US_DCD)
                                uart_handle_dcd_change(port, !(status & ATMEL_US_DCD));
                        if (status_change & ATMEL_US_CTS)
                                uart_handle_cts_change(port, !(status & ATMEL_US_CTS));

                        wake_up_interruptible(&port->state->port.delta_msr_wait);
                }
        }
}

/*
 * Interrupt handler
 */
static irqreturn_t atmel_interrupt(int irq, void *dev_id)
{
        struct uart_port *port = dev_id;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned int status, pending, mask, pass_counter = 0;

        spin_lock(&atmel_port->lock_suspended);

        do {
                status = atmel_get_lines_status(port);
                mask = atmel_uart_readl(port, ATMEL_US_IMR);
                pending = status & mask;
                if (!pending)
                        break;

                if (atmel_port->suspended) {
                        atmel_port->pending |= pending;
                        atmel_port->pending_status = status;
                        atmel_uart_writel(port, ATMEL_US_IDR, mask);
                        pm_system_wakeup();
                        break;
                }

                atmel_handle_receive(port, pending);
                atmel_handle_status(port, pending, status);
                atmel_handle_transmit(port, pending);
        } while (pass_counter++ < ATMEL_ISR_PASS_LIMIT);

        spin_unlock(&atmel_port->lock_suspended);

        return pass_counter ? IRQ_HANDLED : IRQ_NONE;
}

static void atmel_release_tx_pdc(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;

        dma_unmap_single(port->dev,
                         pdc->dma_addr,
                         pdc->dma_size,
                         DMA_TO_DEVICE);
}

/*
 * Called from tasklet with ENDTX and TXBUFE interrupts disabled.
 */
static void atmel_tx_pdc(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct circ_buf *xmit = &port->state->xmit;
        struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;
        int count;

        /* nothing left to transmit? */
        if (atmel_uart_readl(port, ATMEL_PDC_TCR))
                return;

        xmit->tail += pdc->ofs;
        xmit->tail &= UART_XMIT_SIZE - 1;

        port->icount.tx += pdc->ofs;
        pdc->ofs = 0;

        /* more to transmit - setup next transfer */

        /* disable PDC transmit */
        atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);

        if (!uart_circ_empty(xmit) && !uart_tx_stopped(port)) {
                dma_sync_single_for_device(port->dev,
                                           pdc->dma_addr,
                                           pdc->dma_size,
                                           DMA_TO_DEVICE);

                count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
                pdc->ofs = count;

                atmel_uart_writel(port, ATMEL_PDC_TPR,
                                  pdc->dma_addr + xmit->tail);
                atmel_uart_writel(port, ATMEL_PDC_TCR, count);
                /* re-enable PDC transmit */
                atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTEN);
                /* Enable interrupts */
                atmel_uart_writel(port, ATMEL_US_IER,
                                  atmel_port->tx_done_mask);
        } else {
                if ((port->rs485.flags & SER_RS485_ENABLED) &&
                    !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
                        /* DMA done, stop TX, start RX for RS485 */
                        atmel_start_rx(port);
                }
        }

        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(port);
}

static int atmel_prepare_tx_pdc(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;
        struct circ_buf *xmit = &port->state->xmit;

        pdc->buf = xmit->buf;
        pdc->dma_addr = dma_map_single(port->dev,
                                        pdc->buf,
                                        UART_XMIT_SIZE,
                                        DMA_TO_DEVICE);
        pdc->dma_size = UART_XMIT_SIZE;
        pdc->ofs = 0;

        return 0;
}

static void atmel_rx_from_ring(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct circ_buf *ring = &atmel_port->rx_ring;
        unsigned int flg;
        unsigned int status;

        while (ring->head != ring->tail) {
                struct atmel_uart_char c;

                /* Make sure c is loaded after head. */
                smp_rmb();

                c = ((struct atmel_uart_char *)ring->buf)[ring->tail];

                ring->tail = (ring->tail + 1) & (ATMEL_SERIAL_RINGSIZE - 1);

                port->icount.rx++;
                status = c.status;
                flg = TTY_NORMAL;

                /*
                 * note that the error handling code is
                 * out of the main execution path
                 */
                if (unlikely(status & (ATMEL_US_PARE | ATMEL_US_FRAME
                                       | ATMEL_US_OVRE | ATMEL_US_RXBRK))) {
                        if (status & ATMEL_US_RXBRK) {
                                /* ignore side-effect */
                                status &= ~(ATMEL_US_PARE | ATMEL_US_FRAME);

                                port->icount.brk++;
                                if (uart_handle_break(port))
                                        continue;
                        }
                        if (status & ATMEL_US_PARE)
                                port->icount.parity++;
                        if (status & ATMEL_US_FRAME)
                                port->icount.frame++;
                        if (status & ATMEL_US_OVRE)
                                port->icount.overrun++;

                        status &= port->read_status_mask;

                        if (status & ATMEL_US_RXBRK)
                                flg = TTY_BREAK;
                        else if (status & ATMEL_US_PARE)
                                flg = TTY_PARITY;
                        else if (status & ATMEL_US_FRAME)
                                flg = TTY_FRAME;
                }


                if (uart_handle_sysrq_char(port, c.ch))
                        continue;

                uart_insert_char(port, status, ATMEL_US_OVRE, c.ch, flg);
        }

        /*
         * Drop the lock here since it might end up calling
         * uart_start(), which takes the lock.
         */
        spin_unlock(&port->lock);
        tty_flip_buffer_push(&port->state->port);
        spin_lock(&port->lock);
}

static void atmel_release_rx_pdc(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        int i;

        for (i = 0; i < 2; i++) {
                struct atmel_dma_buffer *pdc = &atmel_port->pdc_rx[i];

                dma_unmap_single(port->dev,
                                 pdc->dma_addr,
                                 pdc->dma_size,
                                 DMA_FROM_DEVICE);
                kfree(pdc->buf);
        }
}

static void atmel_rx_from_pdc(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct tty_port *tport = &port->state->port;
        struct atmel_dma_buffer *pdc;
        int rx_idx = atmel_port->pdc_rx_idx;
        unsigned int head;
        unsigned int tail;
        unsigned int count;

        do {
                /* Reset the UART timeout early so that we don't miss one */
                atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_STTTO);

                pdc = &atmel_port->pdc_rx[rx_idx];
                head = atmel_uart_readl(port, ATMEL_PDC_RPR) - pdc->dma_addr;
                tail = pdc->ofs;

                /* If the PDC has switched buffers, RPR won't contain
                 * any address within the current buffer. Since head
                 * is unsigned, we just need a one-way comparison to
                 * find out.
                 *
                 * In this case, we just need to consume the entire
                 * buffer and resubmit it for DMA. This will clear the
                 * ENDRX bit as well, so that we can safely re-enable
                 * all interrupts below.
                 */
                head = min(head, pdc->dma_size);

                if (likely(head != tail)) {
                        dma_sync_single_for_cpu(port->dev, pdc->dma_addr,
                                        pdc->dma_size, DMA_FROM_DEVICE);

                        /*
                         * head will only wrap around when we recycle
                         * the DMA buffer, and when that happens, we
                         * explicitly set tail to 0. So head will
                         * always be greater than tail.
                         */
                        count = head - tail;

                        tty_insert_flip_string(tport, pdc->buf + pdc->ofs,
                                                count);

                        dma_sync_single_for_device(port->dev, pdc->dma_addr,
                                        pdc->dma_size, DMA_FROM_DEVICE);

                        port->icount.rx += count;
                        pdc->ofs = head;
                }

                /*
                 * If the current buffer is full, we need to check if
                 * the next one contains any additional data.
                 */
                if (head >= pdc->dma_size) {
                        pdc->ofs = 0;
                        atmel_uart_writel(port, ATMEL_PDC_RNPR, pdc->dma_addr);
                        atmel_uart_writel(port, ATMEL_PDC_RNCR, pdc->dma_size);

                        rx_idx = !rx_idx;
                        atmel_port->pdc_rx_idx = rx_idx;
                }
        } while (head >= pdc->dma_size);

        /*
         * Drop the lock here since it might end up calling
         * uart_start(), which takes the lock.
         */
        spin_unlock(&port->lock);
        tty_flip_buffer_push(tport);
        spin_lock(&port->lock);

        atmel_uart_writel(port, ATMEL_US_IER,
                          ATMEL_US_ENDRX | ATMEL_US_TIMEOUT);
}

static int atmel_prepare_rx_pdc(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        int i;

        for (i = 0; i < 2; i++) {
                struct atmel_dma_buffer *pdc = &atmel_port->pdc_rx[i];

                pdc->buf = kmalloc(PDC_BUFFER_SIZE, GFP_KERNEL);
                if (pdc->buf == NULL) {
                        if (i != 0) {
                                dma_unmap_single(port->dev,
                                        atmel_port->pdc_rx[0].dma_addr,
                                        PDC_BUFFER_SIZE,
                                        DMA_FROM_DEVICE);
                                kfree(atmel_port->pdc_rx[0].buf);
                        }
                        atmel_port->use_pdc_rx = 0;
                        return -ENOMEM;
                }
                pdc->dma_addr = dma_map_single(port->dev,
                                                pdc->buf,
                                                PDC_BUFFER_SIZE,
                                                DMA_FROM_DEVICE);
                pdc->dma_size = PDC_BUFFER_SIZE;
                pdc->ofs = 0;
        }

        atmel_port->pdc_rx_idx = 0;

        atmel_uart_writel(port, ATMEL_PDC_RPR, atmel_port->pdc_rx[0].dma_addr);
        atmel_uart_writel(port, ATMEL_PDC_RCR, PDC_BUFFER_SIZE);

        atmel_uart_writel(port, ATMEL_PDC_RNPR,
                          atmel_port->pdc_rx[1].dma_addr);
        atmel_uart_writel(port, ATMEL_PDC_RNCR, PDC_BUFFER_SIZE);

        return 0;
}

/*
 * tasklet handling tty stuff outside the interrupt handler.
 */
static void atmel_tasklet_rx_func(unsigned long data)
{
        struct uart_port *port = (struct uart_port *)data;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        /* The interrupt handler does not take the lock */
        spin_lock(&port->lock);
        atmel_port->schedule_rx(port);
        spin_unlock(&port->lock);
}

static void atmel_tasklet_tx_func(unsigned long data)
{
        struct uart_port *port = (struct uart_port *)data;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        /* The interrupt handler does not take the lock */
        spin_lock(&port->lock);
        atmel_port->schedule_tx(port);
        spin_unlock(&port->lock);
}

static void atmel_init_property(struct atmel_uart_port *atmel_port,
                                struct platform_device *pdev)
{
        struct device_node *np = pdev->dev.of_node;

        /* DMA/PDC usage specification */
        if (of_property_read_bool(np, "atmel,use-dma-rx")) {
                if (of_property_read_bool(np, "dmas")) {
                        atmel_port->use_dma_rx  = true;
                        atmel_port->use_pdc_rx  = false;
                } else {
                        atmel_port->use_dma_rx  = false;
                        atmel_port->use_pdc_rx  = true;
                }
        } else {
                atmel_port->use_dma_rx  = false;
                atmel_port->use_pdc_rx  = false;
        }

        if (of_property_read_bool(np, "atmel,use-dma-tx")) {
                if (of_property_read_bool(np, "dmas")) {
                        atmel_port->use_dma_tx  = true;
                        atmel_port->use_pdc_tx  = false;
                } else {
                        atmel_port->use_dma_tx  = false;
                        atmel_port->use_pdc_tx  = true;
                }
        } else {
                atmel_port->use_dma_tx  = false;
                atmel_port->use_pdc_tx  = false;
        }
}

static void atmel_init_rs485(struct uart_port *port,
                                struct platform_device *pdev)
{
        struct device_node *np = pdev->dev.of_node;

        struct serial_rs485 *rs485conf = &port->rs485;
        u32 rs485_delay[2];

        /* rs485 properties */
        if (of_property_read_u32_array(np, "rs485-rts-delay",
                                       rs485_delay, 2) == 0) {
                rs485conf->delay_rts_before_send = rs485_delay[0];
                rs485conf->delay_rts_after_send = rs485_delay[1];
                rs485conf->flags = 0;
        }

        if (of_get_property(np, "rs485-rx-during-tx", NULL))
                rs485conf->flags |= SER_RS485_RX_DURING_TX;

        if (of_get_property(np, "linux,rs485-enabled-at-boot-time", NULL))
                rs485conf->flags |= SER_RS485_ENABLED;
}

static void atmel_set_ops(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (atmel_use_dma_rx(port)) {
                atmel_port->prepare_rx = &atmel_prepare_rx_dma;
                atmel_port->schedule_rx = &atmel_rx_from_dma;
                atmel_port->release_rx = &atmel_release_rx_dma;
        } else if (atmel_use_pdc_rx(port)) {
                atmel_port->prepare_rx = &atmel_prepare_rx_pdc;
                atmel_port->schedule_rx = &atmel_rx_from_pdc;
                atmel_port->release_rx = &atmel_release_rx_pdc;
        } else {
                atmel_port->prepare_rx = NULL;
                atmel_port->schedule_rx = &atmel_rx_from_ring;
                atmel_port->release_rx = NULL;
        }

        if (atmel_use_dma_tx(port)) {
                atmel_port->prepare_tx = &atmel_prepare_tx_dma;
                atmel_port->schedule_tx = &atmel_tx_dma;
                atmel_port->release_tx = &atmel_release_tx_dma;
        } else if (atmel_use_pdc_tx(port)) {
                atmel_port->prepare_tx = &atmel_prepare_tx_pdc;
                atmel_port->schedule_tx = &atmel_tx_pdc;
                atmel_port->release_tx = &atmel_release_tx_pdc;
        } else {
                atmel_port->prepare_tx = NULL;
                atmel_port->schedule_tx = &atmel_tx_chars;
                atmel_port->release_tx = NULL;
        }
}

/*
 * Get ip name usart or uart
 */
static void atmel_get_ip_name(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        int name = atmel_uart_readl(port, ATMEL_US_NAME);
        u32 version;
        u32 usart, dbgu_uart, new_uart;
        /* ASCII decoding for IP version */
        usart = 0x55534152;     /* USAR(T) */
        dbgu_uart = 0x44424755; /* DBGU */
        new_uart = 0x55415254;  /* UART */

        /*
         * Only USART devices from at91sam9260 SOC implement fractional
         * baudrate. It is available for all asynchronous modes, with the
         * following restriction: the sampling clock's duty cycle is not
         * constant.
         */
        atmel_port->has_frac_baudrate = false;
        atmel_port->has_hw_timer = false;

        if (name == new_uart) {
                dev_dbg(port->dev, "Uart with hw timer");
                atmel_port->has_hw_timer = true;
                atmel_port->rtor = ATMEL_UA_RTOR;
        } else if (name == usart) {
                dev_dbg(port->dev, "Usart\n");
                atmel_port->has_frac_baudrate = true;
                atmel_port->has_hw_timer = true;
                atmel_port->rtor = ATMEL_US_RTOR;
        } else if (name == dbgu_uart) {
                dev_dbg(port->dev, "Dbgu or uart without hw timer\n");
        } else {
                /* fallback for older SoCs: use version field */
                version = atmel_uart_readl(port, ATMEL_US_VERSION);
                switch (version) {
                case 0x302:
                case 0x10213:
                        dev_dbg(port->dev, "This version is usart\n");
                        atmel_port->has_frac_baudrate = true;
                        atmel_port->has_hw_timer = true;
                        atmel_port->rtor = ATMEL_US_RTOR;
                        break;
                case 0x203:
                case 0x10202:
                        dev_dbg(port->dev, "This version is uart\n");
                        break;
                default:
                        dev_err(port->dev, "Not supported ip name nor version, set to uart\n");
                }
        }
}

/*
 * Perform initialization and enable port for reception
 */
static int atmel_startup(struct uart_port *port)
{
        struct platform_device *pdev = to_platform_device(port->dev);
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        struct tty_struct *tty = port->state->port.tty;
        int retval;

        /*
         * Ensure that no interrupts are enabled otherwise when
         * request_irq() is called we could get stuck trying to
         * handle an unexpected interrupt
         */
        atmel_uart_writel(port, ATMEL_US_IDR, -1);
        atmel_port->ms_irq_enabled = false;

        /*
         * Allocate the IRQ
         */
        retval = request_irq(port->irq, atmel_interrupt,
                        IRQF_SHARED | IRQF_COND_SUSPEND,
                        tty ? tty->name : "atmel_serial", port);
        if (retval) {
                dev_err(port->dev, "atmel_startup - Can't get irq\n");
                return retval;
        }

        atomic_set(&atmel_port->tasklet_shutdown, 0);
        tasklet_init(&atmel_port->tasklet_rx, atmel_tasklet_rx_func,
                        (unsigned long)port);
        tasklet_init(&atmel_port->tasklet_tx, atmel_tasklet_tx_func,
                        (unsigned long)port);

        /*
         * Initialize DMA (if necessary)
         */
        atmel_init_property(atmel_port, pdev);
        atmel_set_ops(port);

        if (atmel_port->prepare_rx) {
                retval = atmel_port->prepare_rx(port);
                if (retval < 0)
                        atmel_set_ops(port);
        }

        if (atmel_port->prepare_tx) {
                retval = atmel_port->prepare_tx(port);
                if (retval < 0)
                        atmel_set_ops(port);
        }

        /*
         * Enable FIFO when available
         */
        if (atmel_port->fifo_size) {
                unsigned int txrdym = ATMEL_US_ONE_DATA;
                unsigned int rxrdym = ATMEL_US_ONE_DATA;
                unsigned int fmr;

                atmel_uart_writel(port, ATMEL_US_CR,
                                  ATMEL_US_FIFOEN |
                                  ATMEL_US_RXFCLR |
                                  ATMEL_US_TXFLCLR);

                if (atmel_use_dma_tx(port))
                        txrdym = ATMEL_US_FOUR_DATA;

                fmr = ATMEL_US_TXRDYM(txrdym) | ATMEL_US_RXRDYM(rxrdym);
                if (atmel_port->rts_high &&
                    atmel_port->rts_low)
                        fmr |=  ATMEL_US_FRTSC |
                                ATMEL_US_RXFTHRES(atmel_port->rts_high) |
                                ATMEL_US_RXFTHRES2(atmel_port->rts_low);

                atmel_uart_writel(port, ATMEL_US_FMR, fmr);
        }

        /* Save current CSR for comparison in atmel_tasklet_func() */
        atmel_port->irq_status_prev = atmel_get_lines_status(port);

        /*
         * Finally, enable the serial port
         */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
        /* enable xmit & rcvr */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);

        setup_timer(&atmel_port->uart_timer,
                        atmel_uart_timer_callback,
                        (unsigned long)port);

        if (atmel_use_pdc_rx(port)) {
                /* set UART timeout */
                if (!atmel_port->has_hw_timer) {
                        mod_timer(&atmel_port->uart_timer,
                                        jiffies + uart_poll_timeout(port));
                /* set USART timeout */
                } else {
                        atmel_uart_writel(port, atmel_port->rtor,
                                          PDC_RX_TIMEOUT);
                        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_STTTO);

                        atmel_uart_writel(port, ATMEL_US_IER,
                                          ATMEL_US_ENDRX | ATMEL_US_TIMEOUT);
                }
                /* enable PDC controller */
                atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_RXTEN);
        } else if (atmel_use_dma_rx(port)) {
                /* set UART timeout */
                if (!atmel_port->has_hw_timer) {
                        mod_timer(&atmel_port->uart_timer,
                                        jiffies + uart_poll_timeout(port));
                /* set USART timeout */
                } else {
                        atmel_uart_writel(port, atmel_port->rtor,
                                          PDC_RX_TIMEOUT);
                        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_STTTO);

                        atmel_uart_writel(port, ATMEL_US_IER,
                                          ATMEL_US_TIMEOUT);
                }
        } else {
                /* enable receive only */
                atmel_uart_writel(port, ATMEL_US_IER, ATMEL_US_RXRDY);
        }

        return 0;
}

/*
 * Flush any TX data submitted for DMA. Called when the TX circular
 * buffer is reset.
 */
static void atmel_flush_buffer(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (atmel_use_pdc_tx(port)) {
                atmel_uart_writel(port, ATMEL_PDC_TCR, 0);
                atmel_port->pdc_tx.ofs = 0;
        }
        /*
         * in uart_flush_buffer(), the xmit circular buffer has just
         * been cleared, so we have to reset tx_len accordingly.
         */
        atmel_port->tx_len = 0;
}

/*
 * Disable the port
 */
static void atmel_shutdown(struct uart_port *port)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        /* Disable modem control lines interrupts */
        atmel_disable_ms(port);

        /* Disable interrupts at device level */
        atmel_uart_writel(port, ATMEL_US_IDR, -1);

        /* Prevent spurious interrupts from scheduling the tasklet */
        atomic_inc(&atmel_port->tasklet_shutdown);

        /*
         * Prevent any tasklets being scheduled during
         * cleanup
         */
        del_timer_sync(&atmel_port->uart_timer);

        /* Make sure that no interrupt is on the fly */
        synchronize_irq(port->irq);

        /*
         * Clear out any scheduled tasklets before
         * we destroy the buffers
         */
        tasklet_kill(&atmel_port->tasklet_rx);
        tasklet_kill(&atmel_port->tasklet_tx);

        /*
         * Ensure everything is stopped and
         * disable port and break condition.
         */
        atmel_stop_rx(port);
        atmel_stop_tx(port);

        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA);

        /*
         * Shut-down the DMA.
         */
        if (atmel_port->release_rx)
                atmel_port->release_rx(port);
        if (atmel_port->release_tx)
                atmel_port->release_tx(port);

        /*
         * Reset ring buffer pointers
         */
        atmel_port->rx_ring.head = 0;
        atmel_port->rx_ring.tail = 0;

        /*
         * Free the interrupts
         */
        free_irq(port->irq, port);

        atmel_flush_buffer(port);
}

/*
 * Power / Clock management.
 */
static void atmel_serial_pm(struct uart_port *port, unsigned int state,
                            unsigned int oldstate)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        switch (state) {
        case 0:
                /*
                 * Enable the peripheral clock for this serial port.
                 * This is called on uart_open() or a resume event.
                 */
                clk_prepare_enable(atmel_port->clk);

                /* re-enable interrupts if we disabled some on suspend */
                atmel_uart_writel(port, ATMEL_US_IER, atmel_port->backup_imr);
                break;
        case 3:
                /* Back up the interrupt mask and disable all interrupts */
                atmel_port->backup_imr = atmel_uart_readl(port, ATMEL_US_IMR);
                atmel_uart_writel(port, ATMEL_US_IDR, -1);

                /*
                 * Disable the peripheral clock for this serial port.
                 * This is called on uart_close() or a suspend event.
                 */
                clk_disable_unprepare(atmel_port->clk);
                break;
        default:
                dev_err(port->dev, "atmel_serial: unknown pm %d\n", state);
        }
}

/*
 * Change the port parameters
 */
static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
                              struct ktermios *old)
{
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned long flags;
        unsigned int old_mode, mode, imr, quot, baud, div, cd, fp = 0;

        /* save the current mode register */
        mode = old_mode = atmel_uart_readl(port, ATMEL_US_MR);

        /* reset the mode, clock divisor, parity, stop bits and data size */
        mode &= ~(ATMEL_US_USCLKS | ATMEL_US_CHRL | ATMEL_US_NBSTOP |
                  ATMEL_US_PAR | ATMEL_US_USMODE);

        baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 16);

        /* byte size */
        switch (termios->c_cflag & CSIZE) {
        case CS5:
                mode |= ATMEL_US_CHRL_5;
                break;
        case CS6:
                mode |= ATMEL_US_CHRL_6;
                break;
        case CS7:
                mode |= ATMEL_US_CHRL_7;
                break;
        default:
                mode |= ATMEL_US_CHRL_8;
                break;
        }

        /* stop bits */
        if (termios->c_cflag & CSTOPB)
                mode |= ATMEL_US_NBSTOP_2;

        /* parity */
        if (termios->c_cflag & PARENB) {
                /* Mark or Space parity */
                if (termios->c_cflag & CMSPAR) {
                        if (termios->c_cflag & PARODD)
                                mode |= ATMEL_US_PAR_MARK;
                        else
                                mode |= ATMEL_US_PAR_SPACE;
                } else if (termios->c_cflag & PARODD)
                        mode |= ATMEL_US_PAR_ODD;
                else
                        mode |= ATMEL_US_PAR_EVEN;
        } else
                mode |= ATMEL_US_PAR_NONE;

        spin_lock_irqsave(&port->lock, flags);

        port->read_status_mask = ATMEL_US_OVRE;
        if (termios->c_iflag & INPCK)
                port->read_status_mask |= (ATMEL_US_FRAME | ATMEL_US_PARE);
        if (termios->c_iflag & (IGNBRK | BRKINT | PARMRK))
                port->read_status_mask |= ATMEL_US_RXBRK;

        if (atmel_use_pdc_rx(port))
                /* need to enable error interrupts */
                atmel_uart_writel(port, ATMEL_US_IER, port->read_status_mask);

        /*
         * Characters to ignore
         */
        port->ignore_status_mask = 0;
        if (termios->c_iflag & IGNPAR)
                port->ignore_status_mask |= (ATMEL_US_FRAME | ATMEL_US_PARE);
        if (termios->c_iflag & IGNBRK) {
                port->ignore_status_mask |= ATMEL_US_RXBRK;
                /*
                 * If we're ignoring parity and break indicators,
                 * ignore overruns too (for real raw support).
                 */
                if (termios->c_iflag & IGNPAR)
                        port->ignore_status_mask |= ATMEL_US_OVRE;
        }
        /* TODO: Ignore all characters if CREAD is set.*/

        /* update the per-port timeout */
        uart_update_timeout(port, termios->c_cflag, baud);

        /*
         * save/disable interrupts. The tty layer will ensure that the
         * transmitter is empty if requested by the caller, so there's
         * no need to wait for it here.
         */
        imr = atmel_uart_readl(port, ATMEL_US_IMR);
        atmel_uart_writel(port, ATMEL_US_IDR, -1);

        /* disable receiver and transmitter */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS | ATMEL_US_RXDIS);

        /* mode */
        if (port->rs485.flags & SER_RS485_ENABLED) {
                atmel_uart_writel(port, ATMEL_US_TTGR,
                                  port->rs485.delay_rts_after_send);
                mode |= ATMEL_US_USMODE_RS485;
        } else if (termios->c_cflag & CRTSCTS) {
                /* RS232 with hardware handshake (RTS/CTS) */
                if (atmel_use_fifo(port) &&
                    !mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS)) {
                        /*
                         * with ATMEL_US_USMODE_HWHS set, the controller will
                         * be able to drive the RTS pin high/low when the RX
                         * FIFO is above RXFTHRES/below RXFTHRES2.
                         * It will also disable the transmitter when the CTS
                         * pin is high.
                         * This mode is not activated if CTS pin is a GPIO
                         * because in this case, the transmitter is always
                         * disabled (there must be an internal pull-up
                         * responsible for this behaviour).
                         * If the RTS pin is a GPIO, the controller won't be
                         * able to drive it according to the FIFO thresholds,
                         * but it will be handled by the driver.
                         */
                        mode |= ATMEL_US_USMODE_HWHS;
                } else {
                        /*
                         * For platforms without FIFO, the flow control is
                         * handled by the driver.
                         */
                        mode |= ATMEL_US_USMODE_NORMAL;
                }
        } else {
                /* RS232 without hadware handshake */
                mode |= ATMEL_US_USMODE_NORMAL;
        }

        /* set the mode, clock divisor, parity, stop bits and data size */
        atmel_uart_writel(port, ATMEL_US_MR, mode);

        /*
         * when switching the mode, set the RTS line state according to the
         * new mode, otherwise keep the former state
         */
        if ((old_mode & ATMEL_US_USMODE) != (mode & ATMEL_US_USMODE)) {
                unsigned int rts_state;

                if ((mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_HWHS) {
                        /* let the hardware control the RTS line */
                        rts_state = ATMEL_US_RTSDIS;
                } else {
                        /* force RTS line to low level */
                        rts_state = ATMEL_US_RTSEN;
                }

                atmel_uart_writel(port, ATMEL_US_CR, rts_state);
        }

        /*
         * Set the baud rate:
         * Fractional baudrate allows to setup output frequency more
         * accurately. This feature is enabled only when using normal mode.
         * baudrate = selected clock / (8 * (2 - OVER) * (CD + FP / 8))
         * Currently, OVER is always set to 0 so we get
         * baudrate = selected clock / (16 * (CD + FP / 8))
         * then
         * 8 CD + FP = selected clock / (2 * baudrate)
         */
        if (atmel_port->has_frac_baudrate) {
                div = DIV_ROUND_CLOSEST(port->uartclk, baud * 2);
                cd = div >> 3;
                fp = div & ATMEL_US_FP_MASK;
        } else {
                cd = uart_get_divisor(port, baud);
        }

        if (cd > 65535) {       /* BRGR is 16-bit, so switch to slower clock */
                cd /= 8;
                mode |= ATMEL_US_USCLKS_MCK_DIV8;
        }
        quot = cd | fp << ATMEL_US_FP_OFFSET;

        atmel_uart_writel(port, ATMEL_US_BRGR, quot);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);

        /* restore interrupts */
        atmel_uart_writel(port, ATMEL_US_IER, imr);

        /* CTS flow-control and modem-status interrupts */
        if (UART_ENABLE_MS(port, termios->c_cflag))
                atmel_enable_ms(port);
        else
                atmel_disable_ms(port);

        spin_unlock_irqrestore(&port->lock, flags);
}

static void atmel_set_ldisc(struct uart_port *port, struct ktermios *termios)
{
        if (termios->c_line == N_PPS) {
                port->flags |= UPF_HARDPPS_CD;
                spin_lock_irq(&port->lock);
                atmel_enable_ms(port);
                spin_unlock_irq(&port->lock);
        } else {
                port->flags &= ~UPF_HARDPPS_CD;
                if (!UART_ENABLE_MS(port, termios->c_cflag)) {
                        spin_lock_irq(&port->lock);
                        atmel_disable_ms(port);
                        spin_unlock_irq(&port->lock);
                }
        }
}

/*
 * Return string describing the specified port
 */
static const char *atmel_type(struct uart_port *port)
{
        return (port->type == PORT_ATMEL) ? "ATMEL_SERIAL" : NULL;
}

/*
 * Release the memory region(s) being used by 'port'.
 */
static void atmel_release_port(struct uart_port *port)
{
        struct platform_device *pdev = to_platform_device(port->dev);
        int size = pdev->resource[0].end - pdev->resource[0].start + 1;

        release_mem_region(port->mapbase, size);

        if (port->flags & UPF_IOREMAP) {
                iounmap(port->membase);
                port->membase = NULL;
        }
}

/*
 * Request the memory region(s) being used by 'port'.
 */
static int atmel_request_port(struct uart_port *port)
{
        struct platform_device *pdev = to_platform_device(port->dev);
        int size = pdev->resource[0].end - pdev->resource[0].start + 1;

        if (!request_mem_region(port->mapbase, size, "atmel_serial"))
                return -EBUSY;

        if (port->flags & UPF_IOREMAP) {
                port->membase = ioremap(port->mapbase, size);
                if (port->membase == NULL) {
                        release_mem_region(port->mapbase, size);
                        return -ENOMEM;
                }
        }

        return 0;
}

/*
 * Configure/autoconfigure the port.
 */
static void atmel_config_port(struct uart_port *port, int flags)
{
        if (flags & UART_CONFIG_TYPE) {
                port->type = PORT_ATMEL;
                atmel_request_port(port);
        }
}

/*
 * Verify the new serial_struct (for TIOCSSERIAL).
 */
static int atmel_verify_port(struct uart_port *port, struct serial_struct *ser)
{
        int ret = 0;
        if (ser->type != PORT_UNKNOWN && ser->type != PORT_ATMEL)
                ret = -EINVAL;
        if (port->irq != ser->irq)
                ret = -EINVAL;
        if (ser->io_type != SERIAL_IO_MEM)
                ret = -EINVAL;
        if (port->uartclk / 16 != ser->baud_base)
                ret = -EINVAL;
        if (port->mapbase != (unsigned long)ser->iomem_base)
                ret = -EINVAL;
        if (port->iobase != ser->port)
                ret = -EINVAL;
        if (ser->hub6 != 0)
                ret = -EINVAL;
        return ret;
}

#ifdef CONFIG_CONSOLE_POLL
static int atmel_poll_get_char(struct uart_port *port)
{
        while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_RXRDY))
                cpu_relax();

        return atmel_uart_read_char(port);
}

static void atmel_poll_put_char(struct uart_port *port, unsigned char ch)
{
        while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXRDY))
                cpu_relax();

        atmel_uart_write_char(port, ch);
}
#endif

static const struct uart_ops atmel_pops = {
        .tx_empty       = atmel_tx_empty,
        .set_mctrl      = atmel_set_mctrl,
        .get_mctrl      = atmel_get_mctrl,
        .stop_tx        = atmel_stop_tx,
        .start_tx       = atmel_start_tx,
        .stop_rx        = atmel_stop_rx,
        .enable_ms      = atmel_enable_ms,
        .break_ctl      = atmel_break_ctl,
        .startup        = atmel_startup,
        .shutdown       = atmel_shutdown,
        .flush_buffer   = atmel_flush_buffer,
        .set_termios    = atmel_set_termios,
        .set_ldisc      = atmel_set_ldisc,
        .type           = atmel_type,
        .release_port   = atmel_release_port,
        .request_port   = atmel_request_port,
        .config_port    = atmel_config_port,
        .verify_port    = atmel_verify_port,
        .pm             = atmel_serial_pm,
#ifdef CONFIG_CONSOLE_POLL
        .poll_get_char  = atmel_poll_get_char,
        .poll_put_char  = atmel_poll_put_char,
#endif
};

/*
 * Configure the port from the platform device resource info.
 */
static int atmel_init_port(struct atmel_uart_port *atmel_port,
                                      struct platform_device *pdev)
{
        int ret;
        struct uart_port *port = &atmel_port->uart;

        atmel_init_property(atmel_port, pdev);
        atmel_set_ops(port);

        atmel_init_rs485(port, pdev);

        port->iotype            = UPIO_MEM;
        port->flags             = UPF_BOOT_AUTOCONF | UPF_IOREMAP;
        port->ops               = &atmel_pops;
        port->fifosize          = 1;
        port->dev               = &pdev->dev;
        port->mapbase   = pdev->resource[0].start;
        port->irq       = pdev->resource[1].start;
        port->rs485_config      = atmel_config_rs485;
        port->membase   = NULL;

        memset(&atmel_port->rx_ring, 0, sizeof(atmel_port->rx_ring));

        /* for console, the clock could already be configured */
        if (!atmel_port->clk) {
                atmel_port->clk = clk_get(&pdev->dev, "usart");
                if (IS_ERR(atmel_port->clk)) {
                        ret = PTR_ERR(atmel_port->clk);
                        atmel_port->clk = NULL;
                        return ret;
                }
                ret = clk_prepare_enable(atmel_port->clk);
                if (ret) {
                        clk_put(atmel_port->clk);
                        atmel_port->clk = NULL;
                        return ret;
                }
                port->uartclk = clk_get_rate(atmel_port->clk);
                clk_disable_unprepare(atmel_port->clk);
                /* only enable clock when USART is in use */
        }

        /* Use TXEMPTY for interrupt when rs485 else TXRDY or ENDTX|TXBUFE */
        if (port->rs485.flags & SER_RS485_ENABLED)
                atmel_port->tx_done_mask = ATMEL_US_TXEMPTY;
        else if (atmel_use_pdc_tx(port)) {
                port->fifosize = PDC_BUFFER_SIZE;
                atmel_port->tx_done_mask = ATMEL_US_ENDTX | ATMEL_US_TXBUFE;
        } else {
                atmel_port->tx_done_mask = ATMEL_US_TXRDY;
        }

        return 0;
}

#ifdef CONFIG_SERIAL_ATMEL_CONSOLE
static void atmel_console_putchar(struct uart_port *port, int ch)
{
        while (!(atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXRDY))
                cpu_relax();
        atmel_uart_write_char(port, ch);
}

/*
 * Interrupts are disabled on entering
 */
static void atmel_console_write(struct console *co, const char *s, u_int count)
{
        struct uart_port *port = &atmel_ports[co->index].uart;
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned int status, imr;
        unsigned int pdc_tx;

        /*
         * First, save IMR and then disable interrupts
         */
        imr = atmel_uart_readl(port, ATMEL_US_IMR);
        atmel_uart_writel(port, ATMEL_US_IDR,
                          ATMEL_US_RXRDY | atmel_port->tx_done_mask);

        /* Store PDC transmit status and disable it */
        pdc_tx = atmel_uart_readl(port, ATMEL_PDC_PTSR) & ATMEL_PDC_TXTEN;
        atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);

        /* Make sure that tx path is actually able to send characters */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);

        uart_console_write(port, s, count, atmel_console_putchar);

        /*
         * Finally, wait for transmitter to become empty
         * and restore IMR
         */
        do {
                status = atmel_uart_readl(port, ATMEL_US_CSR);
        } while (!(status & ATMEL_US_TXRDY));

        /* Restore PDC transmit status */
        if (pdc_tx)
                atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTEN);

        /* set interrupts back the way they were */
        atmel_uart_writel(port, ATMEL_US_IER, imr);
}

/*
 * If the port was already initialised (eg, by a boot loader),
 * try to determine the current setup.
 */
static void __init atmel_console_get_options(struct uart_port *port, int *baud,
                                             int *parity, int *bits)
{
        unsigned int mr, quot;

        /*
         * If the baud rate generator isn't running, the port wasn't
         * initialized by the boot loader.
         */
        quot = atmel_uart_readl(port, ATMEL_US_BRGR) & ATMEL_US_CD;
        if (!quot)
                return;

        mr = atmel_uart_readl(port, ATMEL_US_MR) & ATMEL_US_CHRL;
        if (mr == ATMEL_US_CHRL_8)
                *bits = 8;
        else
                *bits = 7;

        mr = atmel_uart_readl(port, ATMEL_US_MR) & ATMEL_US_PAR;
        if (mr == ATMEL_US_PAR_EVEN)
                *parity = 'e';
        else if (mr == ATMEL_US_PAR_ODD)
                *parity = 'o';

        /*
         * The serial core only rounds down when matching this to a
         * supported baud rate. Make sure we don't end up slightly
         * lower than one of those, as it would make us fall through
         * to a much lower baud rate than we really want.
         */
        *baud = port->uartclk / (16 * (quot - 1));
}

static int __init atmel_console_setup(struct console *co, char *options)
{
        int ret;
        struct uart_port *port = &atmel_ports[co->index].uart;
        int baud = 115200;
        int bits = 8;
        int parity = 'n';
        int flow = 'n';

        if (port->membase == NULL) {
                /* Port not initialized yet - delay setup */
                return -ENODEV;
        }

        ret = clk_prepare_enable(atmel_ports[co->index].clk);
        if (ret)
                return ret;

        atmel_uart_writel(port, ATMEL_US_IDR, -1);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);

        if (options)
                uart_parse_options(options, &baud, &parity, &bits, &flow);
        else
                atmel_console_get_options(port, &baud, &parity, &bits);

        return uart_set_options(port, co, baud, parity, bits, flow);
}

static struct uart_driver atmel_uart;

static struct console atmel_console = {
        .name           = ATMEL_DEVICENAME,
        .write          = atmel_console_write,
        .device         = uart_console_device,
        .setup          = atmel_console_setup,
        .flags          = CON_PRINTBUFFER,
        .index          = -1,
        .data           = &atmel_uart,
};

#define ATMEL_CONSOLE_DEVICE    (&atmel_console)

static inline bool atmel_is_console_port(struct uart_port *port)
{
        return port->cons && port->cons->index == port->line;
}

#else
#define ATMEL_CONSOLE_DEVICE    NULL

static inline bool atmel_is_console_port(struct uart_port *port)
{
        return false;
}
#endif

static struct uart_driver atmel_uart = {
        .owner          = THIS_MODULE,
        .driver_name    = "atmel_serial",
        .dev_name       = ATMEL_DEVICENAME,
        .major          = SERIAL_ATMEL_MAJOR,
        .minor          = MINOR_START,
        .nr             = ATMEL_MAX_UART,
        .cons           = ATMEL_CONSOLE_DEVICE,
};

#ifdef CONFIG_PM
static bool atmel_serial_clk_will_stop(void)
{
#ifdef CONFIG_ARCH_AT91
        return at91_suspend_entering_slow_clock();
#else
        return false;
#endif
}

static int atmel_serial_suspend(struct platform_device *pdev,
                                pm_message_t state)
{
        struct uart_port *port = platform_get_drvdata(pdev);
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

        if (atmel_is_console_port(port) && console_suspend_enabled) {
                /* Drain the TX shifter */
                while (!(atmel_uart_readl(port, ATMEL_US_CSR) &
                         ATMEL_US_TXEMPTY))
                        cpu_relax();
        }

        if (atmel_is_console_port(port) && !console_suspend_enabled) {
                /* Cache register values as we won't get a full shutdown/startup
                 * cycle
                 */
                atmel_port->cache.mr = atmel_uart_readl(port, ATMEL_US_MR);
                atmel_port->cache.imr = atmel_uart_readl(port, ATMEL_US_IMR);
                atmel_port->cache.brgr = atmel_uart_readl(port, ATMEL_US_BRGR);
                atmel_port->cache.rtor = atmel_uart_readl(port,
                                                          atmel_port->rtor);
                atmel_port->cache.ttgr = atmel_uart_readl(port, ATMEL_US_TTGR);
                atmel_port->cache.fmr = atmel_uart_readl(port, ATMEL_US_FMR);
                atmel_port->cache.fimr = atmel_uart_readl(port, ATMEL_US_FIMR);
        }

        /* we can not wake up if we're running on slow clock */
        atmel_port->may_wakeup = device_may_wakeup(&pdev->dev);
        if (atmel_serial_clk_will_stop()) {
                unsigned long flags;

                spin_lock_irqsave(&atmel_port->lock_suspended, flags);
                atmel_port->suspended = true;
                spin_unlock_irqrestore(&atmel_port->lock_suspended, flags);
                device_set_wakeup_enable(&pdev->dev, 0);
        }

        uart_suspend_port(&atmel_uart, port);

        return 0;
}

static int atmel_serial_resume(struct platform_device *pdev)
{
        struct uart_port *port = platform_get_drvdata(pdev);
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        unsigned long flags;

        if (atmel_is_console_port(port) && !console_suspend_enabled) {
                atmel_uart_writel(port, ATMEL_US_MR, atmel_port->cache.mr);
                atmel_uart_writel(port, ATMEL_US_IER, atmel_port->cache.imr);
                atmel_uart_writel(port, ATMEL_US_BRGR, atmel_port->cache.brgr);
                atmel_uart_writel(port, atmel_port->rtor,
                                  atmel_port->cache.rtor);
                atmel_uart_writel(port, ATMEL_US_TTGR, atmel_port->cache.ttgr);

                if (atmel_port->fifo_size) {
                        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_FIFOEN |
                                          ATMEL_US_RXFCLR | ATMEL_US_TXFLCLR);
                        atmel_uart_writel(port, ATMEL_US_FMR,
                                          atmel_port->cache.fmr);
                        atmel_uart_writel(port, ATMEL_US_FIER,
                                          atmel_port->cache.fimr);
                }
                atmel_start_rx(port);
        }

        spin_lock_irqsave(&atmel_port->lock_suspended, flags);
        if (atmel_port->pending) {
                atmel_handle_receive(port, atmel_port->pending);
                atmel_handle_status(port, atmel_port->pending,
                                    atmel_port->pending_status);
                atmel_handle_transmit(port, atmel_port->pending);
                atmel_port->pending = 0;
        }
        atmel_port->suspended = false;
        spin_unlock_irqrestore(&atmel_port->lock_suspended, flags);

        uart_resume_port(&atmel_uart, port);
        device_set_wakeup_enable(&pdev->dev, atmel_port->may_wakeup);

        return 0;
}
#else
#define atmel_serial_suspend NULL
#define atmel_serial_resume NULL
#endif

static void atmel_serial_probe_fifos(struct atmel_uart_port *atmel_port,
                                     struct platform_device *pdev)
{
        atmel_port->fifo_size = 0;
        atmel_port->rts_low = 0;
        atmel_port->rts_high = 0;

        if (of_property_read_u32(pdev->dev.of_node,
                                 "atmel,fifo-size",
                                 &atmel_port->fifo_size))
                return;

        if (!atmel_port->fifo_size)
                return;

        if (atmel_port->fifo_size < ATMEL_MIN_FIFO_SIZE) {
                atmel_port->fifo_size = 0;
                dev_err(&pdev->dev, "Invalid FIFO size\n");
                return;
        }

        /*
         * 0 <= rts_low <= rts_high <= fifo_size
         * Once their CTS line asserted by the remote peer, some x86 UARTs tend
         * to flush their internal TX FIFO, commonly up to 16 data, before
         * actually stopping to send new data. So we try to set the RTS High
         * Threshold to a reasonably high value respecting this 16 data
         * empirical rule when possible.
         */
        atmel_port->rts_high = max_t(int, atmel_port->fifo_size >> 1,
                               atmel_port->fifo_size - ATMEL_RTS_HIGH_OFFSET);
        atmel_port->rts_low  = max_t(int, atmel_port->fifo_size >> 2,
                               atmel_port->fifo_size - ATMEL_RTS_LOW_OFFSET);

        dev_info(&pdev->dev, "Using FIFO (%u data)\n",
                 atmel_port->fifo_size);
        dev_dbg(&pdev->dev, "RTS High Threshold : %2u data\n",
                atmel_port->rts_high);
        dev_dbg(&pdev->dev, "RTS Low Threshold  : %2u data\n",
                atmel_port->rts_low);
}

static int atmel_serial_probe(struct platform_device *pdev)
{
        struct atmel_uart_port *atmel_port;
        struct device_node *np = pdev->dev.of_node;
        void *data;
        int ret = -ENODEV;
        bool rs485_enabled;

        BUILD_BUG_ON(ATMEL_SERIAL_RINGSIZE & (ATMEL_SERIAL_RINGSIZE - 1));

        ret = of_alias_get_id(np, "serial");
        if (ret < 0)
                /* port id not found in platform data nor device-tree aliases:
                 * auto-enumerate it */
                ret = find_first_zero_bit(atmel_ports_in_use, ATMEL_MAX_UART);

        if (ret >= ATMEL_MAX_UART) {
                ret = -ENODEV;
                goto err;
        }

        if (test_and_set_bit(ret, atmel_ports_in_use)) {
                /* port already in use */
                ret = -EBUSY;
                goto err;
        }

        atmel_port = &atmel_ports[ret];
        atmel_port->backup_imr = 0;
        atmel_port->uart.line = ret;
        atmel_serial_probe_fifos(atmel_port, pdev);

        atomic_set(&atmel_port->tasklet_shutdown, 0);
        spin_lock_init(&atmel_port->lock_suspended);

        ret = atmel_init_port(atmel_port, pdev);
        if (ret)
                goto err_clear_bit;

        atmel_port->gpios = mctrl_gpio_init(&atmel_port->uart, 0);
        if (IS_ERR(atmel_port->gpios)) {
                ret = PTR_ERR(atmel_port->gpios);
                goto err_clear_bit;
        }

        if (!atmel_use_pdc_rx(&atmel_port->uart)) {
                ret = -ENOMEM;
                data = kmalloc(sizeof(struct atmel_uart_char)
                                * ATMEL_SERIAL_RINGSIZE, GFP_KERNEL);
                if (!data)
                        goto err_alloc_ring;
                atmel_port->rx_ring.buf = data;
        }

        rs485_enabled = atmel_port->uart.rs485.flags & SER_RS485_ENABLED;

        ret = uart_add_one_port(&atmel_uart, &atmel_port->uart);
        if (ret)
                goto err_add_port;

#ifdef CONFIG_SERIAL_ATMEL_CONSOLE
        if (atmel_is_console_port(&atmel_port->uart)
                        && ATMEL_CONSOLE_DEVICE->flags & CON_ENABLED) {
                /*
                 * The serial core enabled the clock for us, so undo
                 * the clk_prepare_enable() in atmel_console_setup()
                 */
                clk_disable_unprepare(atmel_port->clk);
        }
#endif

        device_init_wakeup(&pdev->dev, 1);
        platform_set_drvdata(pdev, atmel_port);

        /*
         * The peripheral clock has been disabled by atmel_init_port():
         * enable it before accessing I/O registers
         */
        clk_prepare_enable(atmel_port->clk);

        if (rs485_enabled) {
                atmel_uart_writel(&atmel_port->uart, ATMEL_US_MR,
                                  ATMEL_US_USMODE_NORMAL);
                atmel_uart_writel(&atmel_port->uart, ATMEL_US_CR,
                                  ATMEL_US_RTSEN);
        }

        /*
         * Get port name of usart or uart
         */
        atmel_get_ip_name(&atmel_port->uart);

        /*
         * The peripheral clock can now safely be disabled till the port
         * is used
         */
        clk_disable_unprepare(atmel_port->clk);

        return 0;

err_add_port:
        kfree(atmel_port->rx_ring.buf);
        atmel_port->rx_ring.buf = NULL;
err_alloc_ring:
        if (!atmel_is_console_port(&atmel_port->uart)) {
                clk_put(atmel_port->clk);
                atmel_port->clk = NULL;
        }
err_clear_bit:
        clear_bit(atmel_port->uart.line, atmel_ports_in_use);
err:
        return ret;
}

/*
 * Even if the driver is not modular, it makes sense to be able to
 * unbind a device: there can be many bound devices, and there are
 * situations where dynamic binding and unbinding can be useful.
 *
 * For example, a connected device can require a specific firmware update
 * protocol that needs bitbanging on IO lines, but use the regular serial
 * port in the normal case.
 */
static int atmel_serial_remove(struct platform_device *pdev)
{
        struct uart_port *port = platform_get_drvdata(pdev);
        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        int ret = 0;

        tasklet_kill(&atmel_port->tasklet_rx);
        tasklet_kill(&atmel_port->tasklet_tx);

        device_init_wakeup(&pdev->dev, 0);

        ret = uart_remove_one_port(&atmel_uart, port);

        kfree(atmel_port->rx_ring.buf);

        /* "port" is allocated statically, so we shouldn't free it */

        clear_bit(port->line, atmel_ports_in_use);

        clk_put(atmel_port->clk);
        atmel_port->clk = NULL;

        return ret;
}

static struct platform_driver atmel_serial_driver = {
        .probe          = atmel_serial_probe,
        .remove         = atmel_serial_remove,
        .suspend        = atmel_serial_suspend,
        .resume         = atmel_serial_resume,
        .driver         = {
                .name                   = "atmel_usart",
                .of_match_table         = of_match_ptr(atmel_serial_dt_ids),
        },
};

static int __init atmel_serial_init(void)
{
        int ret;

        ret = uart_register_driver(&atmel_uart);
        if (ret)
                return ret;

        ret = platform_driver_register(&atmel_serial_driver);
        if (ret)
                uart_unregister_driver(&atmel_uart);

        return ret;
}
device_initcall(atmel_serial_init);