/*
 * ARC On-Chip(fpga) UART Driver
 *
 * Copyright (C) 2010-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * vineetg: July 10th 2012
 *  -Decoupled the driver from arch/arc
 *    +Using platform_get_resource() for irq/membase (thx to bfin_uart.c)
 *    +Using early_platform_xxx() for early console (thx to mach-shmobile/xxx)
 *
 * Vineetg: Aug 21st 2010
 *  -Is uart_tx_stopped() not done in tty write path as it has already been
 *   taken care of, in serial core
 *
 * Vineetg: Aug 18th 2010
 *  -New Serial Core based ARC UART driver
 *  -Derived largely from blackfin driver albiet with some major tweaks
 *
 * TODO:
 *  -check if sysreq works
 */

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

#include <linux/module.h>
#include <linux/serial.h>
#include <linux/console.h>
#include <linux/sysrq.h>
#include <linux/platform_device.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/serial_core.h>
#include <linux/io.h>
#include <linux/of_irq.h>
#include <linux/of_address.h>

/*************************************
 * ARC UART Hardware Specs
 ************************************/
#define ARC_UART_TX_FIFO_SIZE  1

/*
 * UART Register set (this is not a Standards Compliant IP)
 * Also each reg is Word aligned, but only 8 bits wide
 */
#define R_ID0   0
#define R_ID1   4
#define R_ID2   8
#define R_ID3   12
#define R_DATA  16
#define R_STS   20
#define R_BAUDL 24
#define R_BAUDH 28

/* Bits for UART Status Reg (R/W) */
#define RXIENB  0x04    /* Receive Interrupt Enable */
#define TXIENB  0x40    /* Transmit Interrupt Enable */

#define RXEMPTY 0x20    /* Receive FIFO Empty: No char receivede */
#define TXEMPTY 0x80    /* Transmit FIFO Empty, thus char can be written into */

#define RXFULL  0x08    /* Receive FIFO full */
#define RXFULL1 0x10    /* Receive FIFO has space for 1 char (tot space=4) */

#define RXFERR  0x01    /* Frame Error: Stop Bit not detected */
#define RXOERR  0x02    /* OverFlow Err: Char recv but RXFULL still set */

/* Uart bit fiddling helpers: lowest level */
#define RBASE(port, reg)      (port->membase + reg)
#define UART_REG_SET(u, r, v) writeb((v), RBASE(u, r))
#define UART_REG_GET(u, r)    readb(RBASE(u, r))

#define UART_REG_OR(u, r, v)  UART_REG_SET(u, r, UART_REG_GET(u, r) | (v))
#define UART_REG_CLR(u, r, v) UART_REG_SET(u, r, UART_REG_GET(u, r) & ~(v))

/* Uart bit fiddling helpers: API level */
#define UART_SET_DATA(uart, val)   UART_REG_SET(uart, R_DATA, val)
#define UART_GET_DATA(uart)        UART_REG_GET(uart, R_DATA)

#define UART_SET_BAUDH(uart, val)  UART_REG_SET(uart, R_BAUDH, val)
#define UART_SET_BAUDL(uart, val)  UART_REG_SET(uart, R_BAUDL, val)

#define UART_CLR_STATUS(uart, val) UART_REG_CLR(uart, R_STS, val)
#define UART_GET_STATUS(uart)      UART_REG_GET(uart, R_STS)

#define UART_ALL_IRQ_DISABLE(uart) UART_REG_CLR(uart, R_STS, RXIENB|TXIENB)
#define UART_RX_IRQ_DISABLE(uart)  UART_REG_CLR(uart, R_STS, RXIENB)
#define UART_TX_IRQ_DISABLE(uart)  UART_REG_CLR(uart, R_STS, TXIENB)

#define UART_ALL_IRQ_ENABLE(uart)  UART_REG_OR(uart, R_STS, RXIENB|TXIENB)
#define UART_RX_IRQ_ENABLE(uart)   UART_REG_OR(uart, R_STS, RXIENB)
#define UART_TX_IRQ_ENABLE(uart)   UART_REG_OR(uart, R_STS, TXIENB)

#define ARC_SERIAL_DEV_NAME     "ttyARC"

struct arc_uart_port {
        struct uart_port port;
        unsigned long baud;
};

#define to_arc_port(uport)  container_of(uport, struct arc_uart_port, port)

static struct arc_uart_port arc_uart_ports[CONFIG_SERIAL_ARC_NR_PORTS];

#ifdef CONFIG_SERIAL_ARC_CONSOLE
static struct console arc_console;
#endif

#define DRIVER_NAME     "arc-uart"

static struct uart_driver arc_uart_driver = {
        .owner          = THIS_MODULE,
        .driver_name    = DRIVER_NAME,
        .dev_name       = ARC_SERIAL_DEV_NAME,
        .major          = 0,
        .minor          = 0,
        .nr             = CONFIG_SERIAL_ARC_NR_PORTS,
#ifdef CONFIG_SERIAL_ARC_CONSOLE
        .cons           = &arc_console,
#endif
};

static void arc_serial_stop_rx(struct uart_port *port)
{
        UART_RX_IRQ_DISABLE(port);
}

static void arc_serial_stop_tx(struct uart_port *port)
{
        while (!(UART_GET_STATUS(port) & TXEMPTY))
                cpu_relax();

        UART_TX_IRQ_DISABLE(port);
}

/*
 * Return TIOCSER_TEMT when transmitter is not busy.
 */
static unsigned int arc_serial_tx_empty(struct uart_port *port)
{
        unsigned int stat;

        stat = UART_GET_STATUS(port);
        if (stat & TXEMPTY)
                return TIOCSER_TEMT;

        return 0;
}

/*
 * Driver internal routine, used by both tty(serial core) as well as tx-isr
 *  -Called under spinlock in either cases
 *  -also tty->stopped has already been checked
 *     = by uart_start( ) before calling us
 *     = tx_ist checks that too before calling
 */
static void arc_serial_tx_chars(struct uart_port *port)
{
        struct circ_buf *xmit = &port->state->xmit;
        int sent = 0;
        unsigned char ch;

        if (unlikely(port->x_char)) {
                UART_SET_DATA(port, port->x_char);
                port->icount.tx++;
                port->x_char = 0;
                sent = 1;
        } else if (!uart_circ_empty(xmit)) {
                ch = xmit->buf[xmit->tail];
                xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
                port->icount.tx++;
                while (!(UART_GET_STATUS(port) & TXEMPTY))
                        cpu_relax();
                UART_SET_DATA(port, ch);
                sent = 1;
        }

        /*
         * If num chars in xmit buffer are too few, ask tty layer for more.
         * By Hard ISR to schedule processing in software interrupt part
         */
        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(port);

        if (sent)
                UART_TX_IRQ_ENABLE(port);
}

/*
 * port is locked and interrupts are disabled
 * uart_start( ) calls us under the port spinlock irqsave
 */
static void arc_serial_start_tx(struct uart_port *port)
{
        arc_serial_tx_chars(port);
}

static void arc_serial_rx_chars(struct uart_port *port, unsigned int status)
{
        unsigned int ch, flg = 0;

        /*
         * UART has 4 deep RX-FIFO. Driver's recongnition of this fact
         * is very subtle. Here's how ...
         * Upon getting a RX-Intr, such that RX-EMPTY=0, meaning data available,
         * driver reads the DATA Reg and keeps doing that in a loop, until
         * RX-EMPTY=1. Multiple chars being avail, with a single Interrupt,
         * before RX-EMPTY=0, implies some sort of buffering going on in the
         * controller, which is indeed the Rx-FIFO.
         */
        do {
                /*
                 * This could be an Rx Intr for err (no data),
                 * so check err and clear that Intr first
                 */
                if (unlikely(status & (RXOERR | RXFERR))) {
                        if (status & RXOERR) {
                                port->icount.overrun++;
                                flg = TTY_OVERRUN;
                                UART_CLR_STATUS(port, RXOERR);
                        }

                        if (status & RXFERR) {
                                port->icount.frame++;
                                flg = TTY_FRAME;
                                UART_CLR_STATUS(port, RXFERR);
                        }
                } else
                        flg = TTY_NORMAL;

                if (status & RXEMPTY)
                        continue;

                ch = UART_GET_DATA(port);
                port->icount.rx++;

                if (!(uart_handle_sysrq_char(port, ch)))
                        uart_insert_char(port, status, RXOERR, ch, flg);

                spin_unlock(&port->lock);
                tty_flip_buffer_push(&port->state->port);
                spin_lock(&port->lock);
        } while (!((status = UART_GET_STATUS(port)) & RXEMPTY));
}

/*
 * A note on the Interrupt handling state machine of this driver
 *
 * kernel printk writes funnel thru the console driver framework and in order
 * to keep things simple as well as efficient, it writes to UART in polled
 * mode, in one shot, and exits.
 *
 * OTOH, Userland output (via tty layer), uses interrupt based writes as there
 * can be undeterministic delay between char writes.
 *
 * Thus Rx-interrupts are always enabled, while tx-interrupts are by default
 * disabled.
 *
 * When tty has some data to send out, serial core calls driver's start_tx
 * which
 *   -checks-if-tty-buffer-has-char-to-send
 *   -writes-data-to-uart
 *   -enable-tx-intr
 *
 * Once data bits are pushed out, controller raises the Tx-room-avail-Interrupt.
 * The first thing Tx ISR does is disable further Tx interrupts (as this could
 * be the last char to send, before settling down into the quiet polled mode).
 * It then calls the exact routine used by tty layer write to send out any
 * more char in tty buffer. In case of sending, it re-enables Tx-intr. In case
 * of no data, it remains disabled.
 * This is how the transmit state machine is dynamically switched on/off
 */

static irqreturn_t arc_serial_isr(int irq, void *dev_id)
{
        struct uart_port *port = dev_id;
        unsigned int status;

        status = UART_GET_STATUS(port);

        /*
         * Single IRQ for both Rx (data available) Tx (room available) Interrupt
         * notifications from the UART Controller.
         * To demultiplex between the two, we check the relevant bits
         */
        if (status & RXIENB) {

                /* already in ISR, no need of xx_irqsave */
                spin_lock(&port->lock);
                arc_serial_rx_chars(port, status);
                spin_unlock(&port->lock);
        }

        if ((status & TXIENB) && (status & TXEMPTY)) {

                /* Unconditionally disable further Tx-Interrupts.
                 * will be enabled by tx_chars() if needed.
                 */
                UART_TX_IRQ_DISABLE(port);

                spin_lock(&port->lock);

                if (!uart_tx_stopped(port))
                        arc_serial_tx_chars(port);

                spin_unlock(&port->lock);
        }

        return IRQ_HANDLED;
}

static unsigned int arc_serial_get_mctrl(struct uart_port *port)
{
        /*
         * Pretend we have a Modem status reg and following bits are
         *  always set, to satify the serial core state machine
         *  (DSR) Data Set Ready
         *  (CTS) Clear To Send
         *  (CAR) Carrier Detect
         */
        return TIOCM_CTS | TIOCM_DSR | TIOCM_CAR;
}

static void arc_serial_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
        /* MCR not present */
}

static void arc_serial_break_ctl(struct uart_port *port, int break_state)
{
        /* ARC UART doesn't support sending Break signal */
}

static int arc_serial_startup(struct uart_port *port)
{
        /* Before we hook up the ISR, Disable all UART Interrupts */
        UART_ALL_IRQ_DISABLE(port);

        if (request_irq(port->irq, arc_serial_isr, 0, "arc uart rx-tx", port)) {
                dev_warn(port->dev, "Unable to attach ARC UART intr\n");
                return -EBUSY;
        }

        UART_RX_IRQ_ENABLE(port); /* Only Rx IRQ enabled to begin with */

        return 0;
}

/* This is not really needed */
static void arc_serial_shutdown(struct uart_port *port)
{
        free_irq(port->irq, port);
}

static void
arc_serial_set_termios(struct uart_port *port, struct ktermios *new,
                       struct ktermios *old)
{
        struct arc_uart_port *uart = to_arc_port(port);
        unsigned int baud, uartl, uarth, hw_val;
        unsigned long flags;

        /*
         * Use the generic handler so that any specially encoded baud rates
         * such as SPD_xx flags or "%B0" can be handled
         * Max Baud I suppose will not be more than current 115K * 4
         * Formula for ARC UART is: hw-val = ((CLK/(BAUD*4)) -1)
         * spread over two 8-bit registers
         */
        baud = uart_get_baud_rate(port, new, old, 0, 460800);

        hw_val = port->uartclk / (uart->baud * 4) - 1;
        uartl = hw_val & 0xFF;
        uarth = (hw_val >> 8) & 0xFF;

        spin_lock_irqsave(&port->lock, flags);

        UART_ALL_IRQ_DISABLE(port);

        UART_SET_BAUDL(port, uartl);
        UART_SET_BAUDH(port, uarth);

        UART_RX_IRQ_ENABLE(port);

        /*
         * UART doesn't support Parity/Hardware Flow Control;
         * Only supports 8N1 character size
         */
        new->c_cflag &= ~(CMSPAR|CRTSCTS|CSIZE);
        new->c_cflag |= CS8;

        if (old)
                tty_termios_copy_hw(new, old);

        /* Don't rewrite B0 */
        if (tty_termios_baud_rate(new))
                tty_termios_encode_baud_rate(new, baud, baud);

        uart_update_timeout(port, new->c_cflag, baud);

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

static const char *arc_serial_type(struct uart_port *port)
{
        return port->type == PORT_ARC ? DRIVER_NAME : NULL;
}

static void arc_serial_release_port(struct uart_port *port)
{
}

static int arc_serial_request_port(struct uart_port *port)
{
        return 0;
}

/*
 * Verify the new serial_struct (for TIOCSSERIAL).
 */
static int
arc_serial_verify_port(struct uart_port *port, struct serial_struct *ser)
{
        if (port->type != PORT_UNKNOWN && ser->type != PORT_ARC)
                return -EINVAL;

        return 0;
}

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

#ifdef CONFIG_CONSOLE_POLL

static void arc_serial_poll_putchar(struct uart_port *port, unsigned char chr)
{
        while (!(UART_GET_STATUS(port) & TXEMPTY))
                cpu_relax();

        UART_SET_DATA(port, chr);
}

static int arc_serial_poll_getchar(struct uart_port *port)
{
        unsigned char chr;

        while (!(UART_GET_STATUS(port) & RXEMPTY))
                cpu_relax();

        chr = UART_GET_DATA(port);
        return chr;
}
#endif

static const struct uart_ops arc_serial_pops = {
        .tx_empty       = arc_serial_tx_empty,
        .set_mctrl      = arc_serial_set_mctrl,
        .get_mctrl      = arc_serial_get_mctrl,
        .stop_tx        = arc_serial_stop_tx,
        .start_tx       = arc_serial_start_tx,
        .stop_rx        = arc_serial_stop_rx,
        .break_ctl      = arc_serial_break_ctl,
        .startup        = arc_serial_startup,
        .shutdown       = arc_serial_shutdown,
        .set_termios    = arc_serial_set_termios,
        .type           = arc_serial_type,
        .release_port   = arc_serial_release_port,
        .request_port   = arc_serial_request_port,
        .config_port    = arc_serial_config_port,
        .verify_port    = arc_serial_verify_port,
#ifdef CONFIG_CONSOLE_POLL
        .poll_put_char = arc_serial_poll_putchar,
        .poll_get_char = arc_serial_poll_getchar,
#endif
};

#ifdef CONFIG_SERIAL_ARC_CONSOLE

static int arc_serial_console_setup(struct console *co, char *options)
{
        struct uart_port *port;
        int baud = 115200;
        int bits = 8;
        int parity = 'n';
        int flow = 'n';

        if (co->index < 0 || co->index >= CONFIG_SERIAL_ARC_NR_PORTS)
                return -ENODEV;

        /*
         * The uart port backing the console (e.g. ttyARC1) might not have been
         * init yet. If so, defer the console setup to after the port.
         */
        port = &arc_uart_ports[co->index].port;
        if (!port->membase)
                return -ENODEV;

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

        /*
         * Serial core will call port->ops->set_termios( )
         * which will set the baud reg
         */
        return uart_set_options(port, co, baud, parity, bits, flow);
}

static void arc_serial_console_putchar(struct uart_port *port, int ch)
{
        while (!(UART_GET_STATUS(port) & TXEMPTY))
                cpu_relax();

        UART_SET_DATA(port, (unsigned char)ch);
}

/*
 * Interrupts are disabled on entering
 */
static void arc_serial_console_write(struct console *co, const char *s,
                                     unsigned int count)
{
        struct uart_port *port = &arc_uart_ports[co->index].port;
        unsigned long flags;

        spin_lock_irqsave(&port->lock, flags);
        uart_console_write(port, s, count, arc_serial_console_putchar);
        spin_unlock_irqrestore(&port->lock, flags);
}

static struct console arc_console = {
        .name   = ARC_SERIAL_DEV_NAME,
        .write  = arc_serial_console_write,
        .device = uart_console_device,
        .setup  = arc_serial_console_setup,
        .flags  = CON_PRINTBUFFER,
        .index  = -1,
        .data   = &arc_uart_driver
};

static void arc_early_serial_write(struct console *con, const char *s,
                                   unsigned int n)
{
        struct earlycon_device *dev = con->data;

        uart_console_write(&dev->port, s, n, arc_serial_console_putchar);
}

static int __init arc_early_console_setup(struct earlycon_device *dev,
                                          const char *opt)
{
        struct uart_port *port = &dev->port;
        unsigned int l, h, hw_val;

        if (!dev->port.membase)
                return -ENODEV;

        hw_val = port->uartclk / (dev->baud * 4) - 1;
        l = hw_val & 0xFF;
        h = (hw_val >> 8) & 0xFF;

        UART_SET_BAUDL(port, l);
        UART_SET_BAUDH(port, h);

        dev->con->write = arc_early_serial_write;
        return 0;
}
OF_EARLYCON_DECLARE(arc_uart, "snps,arc-uart", arc_early_console_setup);

#endif  /* CONFIG_SERIAL_ARC_CONSOLE */

static int arc_serial_probe(struct platform_device *pdev)
{
        struct device_node *np = pdev->dev.of_node;
        struct arc_uart_port *uart;
        struct uart_port *port;
        int dev_id;
        u32 val;

        /* no device tree device */
        if (!np)
                return -ENODEV;

        dev_id = of_alias_get_id(np, "serial");
        if (dev_id < 0)
                dev_id = 0;

        uart = &arc_uart_ports[dev_id];
        port = &uart->port;

        if (of_property_read_u32(np, "clock-frequency", &val)) {
                dev_err(&pdev->dev, "clock-frequency property NOTset\n");
                return -EINVAL;
        }
        port->uartclk = val;

        if (of_property_read_u32(np, "current-speed", &val)) {
                dev_err(&pdev->dev, "current-speed property NOT set\n");
                return -EINVAL;
        }
        uart->baud = val;

        port->membase = of_iomap(np, 0);
        if (!port->membase)
                /* No point of dev_err since UART itself is hosed here */
                return -ENXIO;

        port->irq = irq_of_parse_and_map(np, 0);

        port->dev = &pdev->dev;
        port->iotype = UPIO_MEM;
        port->flags = UPF_BOOT_AUTOCONF;
        port->line = dev_id;
        port->ops = &arc_serial_pops;

        port->fifosize = ARC_UART_TX_FIFO_SIZE;

        /*
         * uart_insert_char( ) uses it in decideding whether to ignore a
         * char or not. Explicitly setting it here, removes the subtelty
         */
        port->ignore_status_mask = 0;

        return uart_add_one_port(&arc_uart_driver, &arc_uart_ports[dev_id].port);
}

static int arc_serial_remove(struct platform_device *pdev)
{
        /* This will never be called */
        return 0;
}

static const struct of_device_id arc_uart_dt_ids[] = {
        { .compatible = "snps,arc-uart" },
        { /* Sentinel */ }
};
MODULE_DEVICE_TABLE(of, arc_uart_dt_ids);

static struct platform_driver arc_platform_driver = {
        .probe = arc_serial_probe,
        .remove = arc_serial_remove,
        .driver = {
                .name = DRIVER_NAME,
                .of_match_table  = arc_uart_dt_ids,
         },
};

static int __init arc_serial_init(void)
{
        int ret;

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

        ret = platform_driver_register(&arc_platform_driver);
        if (ret)
                uart_unregister_driver(&arc_uart_driver);

        return ret;
}

static void __exit arc_serial_exit(void)
{
        platform_driver_unregister(&arc_platform_driver);
        uart_unregister_driver(&arc_uart_driver);
}

module_init(arc_serial_init);
module_exit(arc_serial_exit);

MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:" DRIVER_NAME);
MODULE_AUTHOR("Vineet Gupta");
MODULE_DESCRIPTION("ARC(Synopsys) On-Chip(fpga) serial driver");