/*
 * Copyright (C) 2011-2015 Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
 * Copyright (C) 2016 Hauke Mehrtens <hauke@hauke-m.de>
 *
 * This program is free software; you can distribute it and/or modify it
 * under the terms of the GNU General Public License (Version 2) as
 * published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of_device.h>
#include <linux/clk.h>
#include <linux/io.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/completion.h>
#include <linux/spinlock.h>
#include <linux/err.h>
#include <linux/gpio.h>
#include <linux/pm_runtime.h>
#include <linux/spi/spi.h>

#ifdef CONFIG_LANTIQ
#include <lantiq_soc.h>
#endif

#define LTQ_SPI_RX_IRQ_NAME     "spi_rx"
#define LTQ_SPI_TX_IRQ_NAME     "spi_tx"
#define LTQ_SPI_ERR_IRQ_NAME    "spi_err"
#define LTQ_SPI_FRM_IRQ_NAME    "spi_frm"

#define LTQ_SPI_CLC             0x00
#define LTQ_SPI_PISEL           0x04
#define LTQ_SPI_ID              0x08
#define LTQ_SPI_CON             0x10
#define LTQ_SPI_STAT            0x14
#define LTQ_SPI_WHBSTATE        0x18
#define LTQ_SPI_TB              0x20
#define LTQ_SPI_RB              0x24
#define LTQ_SPI_RXFCON          0x30
#define LTQ_SPI_TXFCON          0x34
#define LTQ_SPI_FSTAT           0x38
#define LTQ_SPI_BRT             0x40
#define LTQ_SPI_BRSTAT          0x44
#define LTQ_SPI_SFCON           0x60
#define LTQ_SPI_SFSTAT          0x64
#define LTQ_SPI_GPOCON          0x70
#define LTQ_SPI_GPOSTAT         0x74
#define LTQ_SPI_FPGO            0x78
#define LTQ_SPI_RXREQ           0x80
#define LTQ_SPI_RXCNT           0x84
#define LTQ_SPI_DMACON          0xec
#define LTQ_SPI_IRNEN           0xf4
#define LTQ_SPI_IRNICR          0xf8
#define LTQ_SPI_IRNCR           0xfc

#define LTQ_SPI_CLC_SMC_S       16      /* Clock divider for sleep mode */
#define LTQ_SPI_CLC_SMC_M       (0xFF << LTQ_SPI_CLC_SMC_S)
#define LTQ_SPI_CLC_RMC_S       8       /* Clock divider for normal run mode */
#define LTQ_SPI_CLC_RMC_M       (0xFF << LTQ_SPI_CLC_RMC_S)
#define LTQ_SPI_CLC_DISS        BIT(1)  /* Disable status bit */
#define LTQ_SPI_CLC_DISR        BIT(0)  /* Disable request bit */

#define LTQ_SPI_ID_TXFS_S       24      /* Implemented TX FIFO size */
#define LTQ_SPI_ID_TXFS_M       (0x3F << LTQ_SPI_ID_TXFS_S)
#define LTQ_SPI_ID_RXFS_S       16      /* Implemented RX FIFO size */
#define LTQ_SPI_ID_RXFS_M       (0x3F << LTQ_SPI_ID_RXFS_S)
#define LTQ_SPI_ID_MOD_S        8       /* Module ID */
#define LTQ_SPI_ID_MOD_M        (0xff << LTQ_SPI_ID_MOD_S)
#define LTQ_SPI_ID_CFG_S        5       /* DMA interface support */
#define LTQ_SPI_ID_CFG_M        (1 << LTQ_SPI_ID_CFG_S)
#define LTQ_SPI_ID_REV_M        0x1F    /* Hardware revision number */

#define LTQ_SPI_CON_BM_S        16      /* Data width selection */
#define LTQ_SPI_CON_BM_M        (0x1F << LTQ_SPI_CON_BM_S)
#define LTQ_SPI_CON_EM          BIT(24) /* Echo mode */
#define LTQ_SPI_CON_IDLE        BIT(23) /* Idle bit value */
#define LTQ_SPI_CON_ENBV        BIT(22) /* Enable byte valid control */
#define LTQ_SPI_CON_RUEN        BIT(12) /* Receive underflow error enable */
#define LTQ_SPI_CON_TUEN        BIT(11) /* Transmit underflow error enable */
#define LTQ_SPI_CON_AEN         BIT(10) /* Abort error enable */
#define LTQ_SPI_CON_REN         BIT(9)  /* Receive overflow error enable */
#define LTQ_SPI_CON_TEN         BIT(8)  /* Transmit overflow error enable */
#define LTQ_SPI_CON_LB          BIT(7)  /* Loopback control */
#define LTQ_SPI_CON_PO          BIT(6)  /* Clock polarity control */
#define LTQ_SPI_CON_PH          BIT(5)  /* Clock phase control */
#define LTQ_SPI_CON_HB          BIT(4)  /* Heading control */
#define LTQ_SPI_CON_RXOFF       BIT(1)  /* Switch receiver off */
#define LTQ_SPI_CON_TXOFF       BIT(0)  /* Switch transmitter off */

#define LTQ_SPI_STAT_RXBV_S     28
#define LTQ_SPI_STAT_RXBV_M     (0x7 << LTQ_SPI_STAT_RXBV_S)
#define LTQ_SPI_STAT_BSY        BIT(13) /* Busy flag */
#define LTQ_SPI_STAT_RUE        BIT(12) /* Receive underflow error flag */
#define LTQ_SPI_STAT_TUE        BIT(11) /* Transmit underflow error flag */
#define LTQ_SPI_STAT_AE         BIT(10) /* Abort error flag */
#define LTQ_SPI_STAT_RE         BIT(9)  /* Receive error flag */
#define LTQ_SPI_STAT_TE         BIT(8)  /* Transmit error flag */
#define LTQ_SPI_STAT_ME         BIT(7)  /* Mode error flag */
#define LTQ_SPI_STAT_MS         BIT(1)  /* Master/slave select bit */
#define LTQ_SPI_STAT_EN         BIT(0)  /* Enable bit */
#define LTQ_SPI_STAT_ERRORS     (LTQ_SPI_STAT_ME | LTQ_SPI_STAT_TE | \
                                 LTQ_SPI_STAT_RE | LTQ_SPI_STAT_AE | \
                                 LTQ_SPI_STAT_TUE | LTQ_SPI_STAT_RUE)

#define LTQ_SPI_WHBSTATE_SETTUE BIT(15) /* Set transmit underflow error flag */
#define LTQ_SPI_WHBSTATE_SETAE  BIT(14) /* Set abort error flag */
#define LTQ_SPI_WHBSTATE_SETRE  BIT(13) /* Set receive error flag */
#define LTQ_SPI_WHBSTATE_SETTE  BIT(12) /* Set transmit error flag */
#define LTQ_SPI_WHBSTATE_CLRTUE BIT(11) /* Clear transmit underflow error flag */
#define LTQ_SPI_WHBSTATE_CLRAE  BIT(10) /* Clear abort error flag */
#define LTQ_SPI_WHBSTATE_CLRRE  BIT(9)  /* Clear receive error flag */
#define LTQ_SPI_WHBSTATE_CLRTE  BIT(8)  /* Clear transmit error flag */
#define LTQ_SPI_WHBSTATE_SETME  BIT(7)  /* Set mode error flag */
#define LTQ_SPI_WHBSTATE_CLRME  BIT(6)  /* Clear mode error flag */
#define LTQ_SPI_WHBSTATE_SETRUE BIT(5)  /* Set receive underflow error flag */
#define LTQ_SPI_WHBSTATE_CLRRUE BIT(4)  /* Clear receive underflow error flag */
#define LTQ_SPI_WHBSTATE_SETMS  BIT(3)  /* Set master select bit */
#define LTQ_SPI_WHBSTATE_CLRMS  BIT(2)  /* Clear master select bit */
#define LTQ_SPI_WHBSTATE_SETEN  BIT(1)  /* Set enable bit (operational mode) */
#define LTQ_SPI_WHBSTATE_CLREN  BIT(0)  /* Clear enable bit (config mode */
#define LTQ_SPI_WHBSTATE_CLR_ERRORS     (LTQ_SPI_WHBSTATE_CLRRUE | \
                                         LTQ_SPI_WHBSTATE_CLRME | \
                                         LTQ_SPI_WHBSTATE_CLRTE | \
                                         LTQ_SPI_WHBSTATE_CLRRE | \
                                         LTQ_SPI_WHBSTATE_CLRAE | \
                                         LTQ_SPI_WHBSTATE_CLRTUE)

#define LTQ_SPI_RXFCON_RXFITL_S 8       /* FIFO interrupt trigger level */
#define LTQ_SPI_RXFCON_RXFITL_M (0x3F << LTQ_SPI_RXFCON_RXFITL_S)
#define LTQ_SPI_RXFCON_RXFLU    BIT(1)  /* FIFO flush */
#define LTQ_SPI_RXFCON_RXFEN    BIT(0)  /* FIFO enable */

#define LTQ_SPI_TXFCON_TXFITL_S 8       /* FIFO interrupt trigger level */
#define LTQ_SPI_TXFCON_TXFITL_M (0x3F << LTQ_SPI_TXFCON_TXFITL_S)
#define LTQ_SPI_TXFCON_TXFLU    BIT(1)  /* FIFO flush */
#define LTQ_SPI_TXFCON_TXFEN    BIT(0)  /* FIFO enable */

#define LTQ_SPI_FSTAT_RXFFL_S   0
#define LTQ_SPI_FSTAT_RXFFL_M   (0x3f << LTQ_SPI_FSTAT_RXFFL_S)
#define LTQ_SPI_FSTAT_TXFFL_S   8
#define LTQ_SPI_FSTAT_TXFFL_M   (0x3f << LTQ_SPI_FSTAT_TXFFL_S)

#define LTQ_SPI_GPOCON_ISCSBN_S 8
#define LTQ_SPI_GPOCON_INVOUTN_S        0

#define LTQ_SPI_FGPO_SETOUTN_S  8
#define LTQ_SPI_FGPO_CLROUTN_S  0

#define LTQ_SPI_RXREQ_RXCNT_M   0xFFFF  /* Receive count value */
#define LTQ_SPI_RXCNT_TODO_M    0xFFFF  /* Recevie to-do value */

#define LTQ_SPI_IRNEN_TFI       BIT(4)  /* TX finished interrupt */
#define LTQ_SPI_IRNEN_F         BIT(3)  /* Frame end interrupt request */
#define LTQ_SPI_IRNEN_E         BIT(2)  /* Error end interrupt request */
#define LTQ_SPI_IRNEN_T_XWAY    BIT(1)  /* Transmit end interrupt request */
#define LTQ_SPI_IRNEN_R_XWAY    BIT(0)  /* Receive end interrupt request */
#define LTQ_SPI_IRNEN_R_XRX     BIT(1)  /* Transmit end interrupt request */
#define LTQ_SPI_IRNEN_T_XRX     BIT(0)  /* Receive end interrupt request */
#define LTQ_SPI_IRNEN_ALL       0x1F

struct lantiq_ssc_hwcfg {
        unsigned int irnen_r;
        unsigned int irnen_t;
};

struct lantiq_ssc_spi {
        struct spi_master               *master;
        struct device                   *dev;
        void __iomem                    *regbase;
        struct clk                      *spi_clk;
        struct clk                      *fpi_clk;
        const struct lantiq_ssc_hwcfg   *hwcfg;

        spinlock_t                      lock;
        struct workqueue_struct         *wq;
        struct work_struct              work;

        const u8                        *tx;
        u8                              *rx;
        unsigned int                    tx_todo;
        unsigned int                    rx_todo;
        unsigned int                    bits_per_word;
        unsigned int                    speed_hz;
        unsigned int                    tx_fifo_size;
        unsigned int                    rx_fifo_size;
        unsigned int                    base_cs;
};

static u32 lantiq_ssc_readl(const struct lantiq_ssc_spi *spi, u32 reg)
{
        return __raw_readl(spi->regbase + reg);
}

static void lantiq_ssc_writel(const struct lantiq_ssc_spi *spi, u32 val,
                              u32 reg)
{
        __raw_writel(val, spi->regbase + reg);
}

static void lantiq_ssc_maskl(const struct lantiq_ssc_spi *spi, u32 clr,
                             u32 set, u32 reg)
{
        u32 val = __raw_readl(spi->regbase + reg);

        val &= ~clr;
        val |= set;
        __raw_writel(val, spi->regbase + reg);
}

static unsigned int tx_fifo_level(const struct lantiq_ssc_spi *spi)
{
        u32 fstat = lantiq_ssc_readl(spi, LTQ_SPI_FSTAT);

        return (fstat & LTQ_SPI_FSTAT_TXFFL_M) >> LTQ_SPI_FSTAT_TXFFL_S;
}

static unsigned int rx_fifo_level(const struct lantiq_ssc_spi *spi)
{
        u32 fstat = lantiq_ssc_readl(spi, LTQ_SPI_FSTAT);

        return fstat & LTQ_SPI_FSTAT_RXFFL_M;
}

static unsigned int tx_fifo_free(const struct lantiq_ssc_spi *spi)
{
        return spi->tx_fifo_size - tx_fifo_level(spi);
}

static void rx_fifo_reset(const struct lantiq_ssc_spi *spi)
{
        u32 val = spi->rx_fifo_size << LTQ_SPI_RXFCON_RXFITL_S;

        val |= LTQ_SPI_RXFCON_RXFEN | LTQ_SPI_RXFCON_RXFLU;
        lantiq_ssc_writel(spi, val, LTQ_SPI_RXFCON);
}

static void tx_fifo_reset(const struct lantiq_ssc_spi *spi)
{
        u32 val = 1 << LTQ_SPI_TXFCON_TXFITL_S;

        val |= LTQ_SPI_TXFCON_TXFEN | LTQ_SPI_TXFCON_TXFLU;
        lantiq_ssc_writel(spi, val, LTQ_SPI_TXFCON);
}

static void rx_fifo_flush(const struct lantiq_ssc_spi *spi)
{
        lantiq_ssc_maskl(spi, 0, LTQ_SPI_RXFCON_RXFLU, LTQ_SPI_RXFCON);
}

static void tx_fifo_flush(const struct lantiq_ssc_spi *spi)
{
        lantiq_ssc_maskl(spi, 0, LTQ_SPI_TXFCON_TXFLU, LTQ_SPI_TXFCON);
}

static void hw_enter_config_mode(const struct lantiq_ssc_spi *spi)
{
        lantiq_ssc_writel(spi, LTQ_SPI_WHBSTATE_CLREN, LTQ_SPI_WHBSTATE);
}

static void hw_enter_active_mode(const struct lantiq_ssc_spi *spi)
{
        lantiq_ssc_writel(spi, LTQ_SPI_WHBSTATE_SETEN, LTQ_SPI_WHBSTATE);
}

static void hw_setup_speed_hz(const struct lantiq_ssc_spi *spi,
                              unsigned int max_speed_hz)
{
        u32 spi_clk, brt;

        /*
         * SPI module clock is derived from FPI bus clock dependent on
         * divider value in CLC.RMS which is always set to 1.
         *
         *                 f_SPI
         * baudrate = --------------
         *             2 * (BR + 1)
         */
        spi_clk = clk_get_rate(spi->fpi_clk) / 2;

        if (max_speed_hz > spi_clk)
                brt = 0;
        else
                brt = spi_clk / max_speed_hz - 1;

        if (brt > 0xFFFF)
                brt = 0xFFFF;

        dev_dbg(spi->dev, "spi_clk %u, max_speed_hz %u, brt %u\n",
                spi_clk, max_speed_hz, brt);

        lantiq_ssc_writel(spi, brt, LTQ_SPI_BRT);
}

static void hw_setup_bits_per_word(const struct lantiq_ssc_spi *spi,
                                   unsigned int bits_per_word)
{
        u32 bm;

        /* CON.BM value = bits_per_word - 1 */
        bm = (bits_per_word - 1) << LTQ_SPI_CON_BM_S;

        lantiq_ssc_maskl(spi, LTQ_SPI_CON_BM_M, bm, LTQ_SPI_CON);
}

static void hw_setup_clock_mode(const struct lantiq_ssc_spi *spi,
                                unsigned int mode)
{
        u32 con_set = 0, con_clr = 0;

        /*
         * SPI mode mapping in CON register:
         * Mode CPOL CPHA CON.PO CON.PH
         *  0    0    0      0      1
         *  1    0    1      0      0
         *  2    1    0      1      1
         *  3    1    1      1      0
         */
        if (mode & SPI_CPHA)
                con_clr |= LTQ_SPI_CON_PH;
        else
                con_set |= LTQ_SPI_CON_PH;

        if (mode & SPI_CPOL)
                con_set |= LTQ_SPI_CON_PO | LTQ_SPI_CON_IDLE;
        else
                con_clr |= LTQ_SPI_CON_PO | LTQ_SPI_CON_IDLE;

        /* Set heading control */
        if (mode & SPI_LSB_FIRST)
                con_clr |= LTQ_SPI_CON_HB;
        else
                con_set |= LTQ_SPI_CON_HB;

        /* Set loopback mode */
        if (mode & SPI_LOOP)
                con_set |= LTQ_SPI_CON_LB;
        else
                con_clr |= LTQ_SPI_CON_LB;

        lantiq_ssc_maskl(spi, con_clr, con_set, LTQ_SPI_CON);
}

static void lantiq_ssc_hw_init(const struct lantiq_ssc_spi *spi)
{
        const struct lantiq_ssc_hwcfg *hwcfg = spi->hwcfg;

        /*
         * Set clock divider for run mode to 1 to
         * run at same frequency as FPI bus
         */
        lantiq_ssc_writel(spi, 1 << LTQ_SPI_CLC_RMC_S, LTQ_SPI_CLC);

        /* Put controller into config mode */
        hw_enter_config_mode(spi);

        /* Clear error flags */
        lantiq_ssc_maskl(spi, 0, LTQ_SPI_WHBSTATE_CLR_ERRORS, LTQ_SPI_WHBSTATE);

        /* Enable error checking, disable TX/RX */
        lantiq_ssc_writel(spi, LTQ_SPI_CON_RUEN | LTQ_SPI_CON_AEN |
                LTQ_SPI_CON_TEN | LTQ_SPI_CON_REN | LTQ_SPI_CON_TXOFF |
                LTQ_SPI_CON_RXOFF, LTQ_SPI_CON);

        /* Setup default SPI mode */
        hw_setup_bits_per_word(spi, spi->bits_per_word);
        hw_setup_clock_mode(spi, SPI_MODE_0);

        /* Enable master mode and clear error flags */
        lantiq_ssc_writel(spi, LTQ_SPI_WHBSTATE_SETMS |
                               LTQ_SPI_WHBSTATE_CLR_ERRORS,
                               LTQ_SPI_WHBSTATE);

        /* Reset GPIO/CS registers */
        lantiq_ssc_writel(spi, 0, LTQ_SPI_GPOCON);
        lantiq_ssc_writel(spi, 0xFF00, LTQ_SPI_FPGO);

        /* Enable and flush FIFOs */
        rx_fifo_reset(spi);
        tx_fifo_reset(spi);

        /* Enable interrupts */
        lantiq_ssc_writel(spi, hwcfg->irnen_t | hwcfg->irnen_r |
                          LTQ_SPI_IRNEN_E, LTQ_SPI_IRNEN);
}

static int lantiq_ssc_setup(struct spi_device *spidev)
{
        struct spi_master *master = spidev->master;
        struct lantiq_ssc_spi *spi = spi_master_get_devdata(master);
        unsigned int cs = spidev->chip_select;
        u32 gpocon;

        /* GPIOs are used for CS */
        if (gpio_is_valid(spidev->cs_gpio))
                return 0;

        dev_dbg(spi->dev, "using internal chipselect %u\n", cs);

        if (cs < spi->base_cs) {
                dev_err(spi->dev,
                        "chipselect %i too small (min %i)\n", cs, spi->base_cs);
                return -EINVAL;
        }

        /* set GPO pin to CS mode */
        gpocon = 1 << ((cs - spi->base_cs) + LTQ_SPI_GPOCON_ISCSBN_S);

        /* invert GPO pin */
        if (spidev->mode & SPI_CS_HIGH)
                gpocon |= 1 << (cs - spi->base_cs);

        lantiq_ssc_maskl(spi, 0, gpocon, LTQ_SPI_GPOCON);

        return 0;
}

static int lantiq_ssc_prepare_message(struct spi_master *master,
                                      struct spi_message *message)
{
        struct lantiq_ssc_spi *spi = spi_master_get_devdata(master);

        hw_enter_config_mode(spi);
        hw_setup_clock_mode(spi, message->spi->mode);
        hw_enter_active_mode(spi);

        return 0;
}

static void hw_setup_transfer(struct lantiq_ssc_spi *spi,
                              struct spi_device *spidev, struct spi_transfer *t)
{
        unsigned int speed_hz = t->speed_hz;
        unsigned int bits_per_word = t->bits_per_word;
        u32 con;

        if (bits_per_word != spi->bits_per_word ||
                speed_hz != spi->speed_hz) {
                hw_enter_config_mode(spi);
                hw_setup_speed_hz(spi, speed_hz);
                hw_setup_bits_per_word(spi, bits_per_word);
                hw_enter_active_mode(spi);

                spi->speed_hz = speed_hz;
                spi->bits_per_word = bits_per_word;
        }

        /* Configure transmitter and receiver */
        con = lantiq_ssc_readl(spi, LTQ_SPI_CON);
        if (t->tx_buf)
                con &= ~LTQ_SPI_CON_TXOFF;
        else
                con |= LTQ_SPI_CON_TXOFF;

        if (t->rx_buf)
                con &= ~LTQ_SPI_CON_RXOFF;
        else
                con |= LTQ_SPI_CON_RXOFF;

        lantiq_ssc_writel(spi, con, LTQ_SPI_CON);
}

static int lantiq_ssc_unprepare_message(struct spi_master *master,
                                        struct spi_message *message)
{
        struct lantiq_ssc_spi *spi = spi_master_get_devdata(master);

        flush_workqueue(spi->wq);

        /* Disable transmitter and receiver while idle */
        lantiq_ssc_maskl(spi, 0, LTQ_SPI_CON_TXOFF | LTQ_SPI_CON_RXOFF,
                         LTQ_SPI_CON);

        return 0;
}

static void tx_fifo_write(struct lantiq_ssc_spi *spi)
{
        const u8 *tx8;
        const u16 *tx16;
        const u32 *tx32;
        u32 data;
        unsigned int tx_free = tx_fifo_free(spi);

        while (spi->tx_todo && tx_free) {
                switch (spi->bits_per_word) {
                case 2 ... 8:
                        tx8 = spi->tx;
                        data = *tx8;
                        spi->tx_todo--;
                        spi->tx++;
                        break;
                case 16:
                        tx16 = (u16 *) spi->tx;
                        data = *tx16;
                        spi->tx_todo -= 2;
                        spi->tx += 2;
                        break;
                case 32:
                        tx32 = (u32 *) spi->tx;
                        data = *tx32;
                        spi->tx_todo -= 4;
                        spi->tx += 4;
                        break;
                default:
                        WARN_ON(1);
                        data = 0;
                        break;
                }

                lantiq_ssc_writel(spi, data, LTQ_SPI_TB);
                tx_free--;
        }
}

static void rx_fifo_read_full_duplex(struct lantiq_ssc_spi *spi)
{
        u8 *rx8;
        u16 *rx16;
        u32 *rx32;
        u32 data;
        unsigned int rx_fill = rx_fifo_level(spi);

        while (rx_fill) {
                data = lantiq_ssc_readl(spi, LTQ_SPI_RB);

                switch (spi->bits_per_word) {
                case 2 ... 8:
                        rx8 = spi->rx;
                        *rx8 = data;
                        spi->rx_todo--;
                        spi->rx++;
                        break;
                case 16:
                        rx16 = (u16 *) spi->rx;
                        *rx16 = data;
                        spi->rx_todo -= 2;
                        spi->rx += 2;
                        break;
                case 32:
                        rx32 = (u32 *) spi->rx;
                        *rx32 = data;
                        spi->rx_todo -= 4;
                        spi->rx += 4;
                        break;
                default:
                        WARN_ON(1);
                        break;
                }

                rx_fill--;
        }
}

static void rx_fifo_read_half_duplex(struct lantiq_ssc_spi *spi)
{
        u32 data, *rx32;
        u8 *rx8;
        unsigned int rxbv, shift;
        unsigned int rx_fill = rx_fifo_level(spi);

        /*
         * In RX-only mode the bits per word value is ignored by HW. A value
         * of 32 is used instead. Thus all 4 bytes per FIFO must be read.
         * If remaining RX bytes are less than 4, the FIFO must be read
         * differently. The amount of received and valid bytes is indicated
         * by STAT.RXBV register value.
         */
        while (rx_fill) {
                if (spi->rx_todo < 4)  {
                        rxbv = (lantiq_ssc_readl(spi, LTQ_SPI_STAT) &
                                LTQ_SPI_STAT_RXBV_M) >> LTQ_SPI_STAT_RXBV_S;
                        data = lantiq_ssc_readl(spi, LTQ_SPI_RB);

                        shift = (rxbv - 1) * 8;
                        rx8 = spi->rx;

                        while (rxbv) {
                                *rx8++ = (data >> shift) & 0xFF;
                                rxbv--;
                                shift -= 8;
                                spi->rx_todo--;
                                spi->rx++;
                        }
                } else {
                        data = lantiq_ssc_readl(spi, LTQ_SPI_RB);
                        rx32 = (u32 *) spi->rx;

                        *rx32++ = data;
                        spi->rx_todo -= 4;
                        spi->rx += 4;
                }
                rx_fill--;
        }
}

static void rx_request(struct lantiq_ssc_spi *spi)
{
        unsigned int rxreq, rxreq_max;

        /*
         * To avoid receive overflows at high clocks it is better to request
         * only the amount of bytes that fits into all FIFOs. This value
         * depends on the FIFO size implemented in hardware.
         */
        rxreq = spi->rx_todo;
        rxreq_max = spi->rx_fifo_size * 4;
        if (rxreq > rxreq_max)
                rxreq = rxreq_max;

        lantiq_ssc_writel(spi, rxreq, LTQ_SPI_RXREQ);
}

static irqreturn_t lantiq_ssc_xmit_interrupt(int irq, void *data)
{
        struct lantiq_ssc_spi *spi = data;

        if (spi->tx) {
                if (spi->rx && spi->rx_todo)
                        rx_fifo_read_full_duplex(spi);

                if (spi->tx_todo)
                        tx_fifo_write(spi);
                else if (!tx_fifo_level(spi))
                        goto completed;
        } else if (spi->rx) {
                if (spi->rx_todo) {
                        rx_fifo_read_half_duplex(spi);

                        if (spi->rx_todo)
                                rx_request(spi);
                        else
                                goto completed;
                } else {
                        goto completed;
                }
        }

        return IRQ_HANDLED;

completed:
        queue_work(spi->wq, &spi->work);

        return IRQ_HANDLED;
}

static irqreturn_t lantiq_ssc_err_interrupt(int irq, void *data)
{
        struct lantiq_ssc_spi *spi = data;
        u32 stat = lantiq_ssc_readl(spi, LTQ_SPI_STAT);

        if (!(stat & LTQ_SPI_STAT_ERRORS))
                return IRQ_NONE;

        if (stat & LTQ_SPI_STAT_RUE)
                dev_err(spi->dev, "receive underflow error\n");
        if (stat & LTQ_SPI_STAT_TUE)
                dev_err(spi->dev, "transmit underflow error\n");
        if (stat & LTQ_SPI_STAT_AE)
                dev_err(spi->dev, "abort error\n");
        if (stat & LTQ_SPI_STAT_RE)
                dev_err(spi->dev, "receive overflow error\n");
        if (stat & LTQ_SPI_STAT_TE)
                dev_err(spi->dev, "transmit overflow error\n");
        if (stat & LTQ_SPI_STAT_ME)
                dev_err(spi->dev, "mode error\n");

        /* Clear error flags */
        lantiq_ssc_maskl(spi, 0, LTQ_SPI_WHBSTATE_CLR_ERRORS, LTQ_SPI_WHBSTATE);

        /* set bad status so it can be retried */
        if (spi->master->cur_msg)
                spi->master->cur_msg->status = -EIO;
        queue_work(spi->wq, &spi->work);

        return IRQ_HANDLED;
}

static int transfer_start(struct lantiq_ssc_spi *spi, struct spi_device *spidev,
                          struct spi_transfer *t)
{
        unsigned long flags;

        spin_lock_irqsave(&spi->lock, flags);

        spi->tx = t->tx_buf;
        spi->rx = t->rx_buf;

        if (t->tx_buf) {
                spi->tx_todo = t->len;

                /* initially fill TX FIFO */
                tx_fifo_write(spi);
        }

        if (spi->rx) {
                spi->rx_todo = t->len;

                /* start shift clock in RX-only mode */
                if (!spi->tx)
                        rx_request(spi);
        }

        spin_unlock_irqrestore(&spi->lock, flags);

        return t->len;
}

/*
 * The driver only gets an interrupt when the FIFO is empty, but there
 * is an additional shift register from which the data is written to
 * the wire. We get the last interrupt when the controller starts to
 * write the last word to the wire, not when it is finished. Do busy
 * waiting till it finishes.
 */
static void lantiq_ssc_bussy_work(struct work_struct *work)
{
        struct lantiq_ssc_spi *spi;
        unsigned long long timeout = 8LL * 1000LL;
        unsigned long end;

        spi = container_of(work, typeof(*spi), work);

        do_div(timeout, spi->speed_hz);
        timeout += timeout + 100; /* some tolerance */

        end = jiffies + msecs_to_jiffies(timeout);
        do {
                u32 stat = lantiq_ssc_readl(spi, LTQ_SPI_STAT);

                if (!(stat & LTQ_SPI_STAT_BSY)) {
                        spi_finalize_current_transfer(spi->master);
                        return;
                }

                cond_resched();
        } while (!time_after_eq(jiffies, end));

        if (spi->master->cur_msg)
                spi->master->cur_msg->status = -EIO;
        spi_finalize_current_transfer(spi->master);
}

static void lantiq_ssc_handle_err(struct spi_master *master,
                                  struct spi_message *message)
{
        struct lantiq_ssc_spi *spi = spi_master_get_devdata(master);

        /* flush FIFOs on timeout */
        rx_fifo_flush(spi);
        tx_fifo_flush(spi);
}

static void lantiq_ssc_set_cs(struct spi_device *spidev, bool enable)
{
        struct lantiq_ssc_spi *spi = spi_master_get_devdata(spidev->master);
        unsigned int cs = spidev->chip_select;
        u32 fgpo;

        if (!!(spidev->mode & SPI_CS_HIGH) == enable)
                fgpo = (1 << (cs - spi->base_cs));
        else
                fgpo = (1 << (cs - spi->base_cs + LTQ_SPI_FGPO_SETOUTN_S));

        lantiq_ssc_writel(spi, fgpo, LTQ_SPI_FPGO);
}

static int lantiq_ssc_transfer_one(struct spi_master *master,
                                   struct spi_device *spidev,
                                   struct spi_transfer *t)
{
        struct lantiq_ssc_spi *spi = spi_master_get_devdata(master);

        hw_setup_transfer(spi, spidev, t);

        return transfer_start(spi, spidev, t);
}

static const struct lantiq_ssc_hwcfg lantiq_ssc_xway = {
        .irnen_r = LTQ_SPI_IRNEN_R_XWAY,
        .irnen_t = LTQ_SPI_IRNEN_T_XWAY,
};

static const struct lantiq_ssc_hwcfg lantiq_ssc_xrx = {
        .irnen_r = LTQ_SPI_IRNEN_R_XRX,
        .irnen_t = LTQ_SPI_IRNEN_T_XRX,
};

static const struct of_device_id lantiq_ssc_match[] = {
        { .compatible = "lantiq,ase-spi", .data = &lantiq_ssc_xway, },
        { .compatible = "lantiq,falcon-spi", .data = &lantiq_ssc_xrx, },
        { .compatible = "lantiq,xrx100-spi", .data = &lantiq_ssc_xrx, },
        {},
};
MODULE_DEVICE_TABLE(of, lantiq_ssc_match);

static int lantiq_ssc_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct spi_master *master;
        struct resource *res;
        struct lantiq_ssc_spi *spi;
        const struct lantiq_ssc_hwcfg *hwcfg;
        const struct of_device_id *match;
        int err, rx_irq, tx_irq, err_irq;
        u32 id, supports_dma, revision;
        unsigned int num_cs;

        match = of_match_device(lantiq_ssc_match, dev);
        if (!match) {
                dev_err(dev, "no device match\n");
                return -EINVAL;
        }
        hwcfg = match->data;

        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (!res) {
                dev_err(dev, "failed to get resources\n");
                return -ENXIO;
        }

        rx_irq = platform_get_irq_byname(pdev, LTQ_SPI_RX_IRQ_NAME);
        if (rx_irq < 0) {
                dev_err(dev, "failed to get %s\n", LTQ_SPI_RX_IRQ_NAME);
                return -ENXIO;
        }

        tx_irq = platform_get_irq_byname(pdev, LTQ_SPI_TX_IRQ_NAME);
        if (tx_irq < 0) {
                dev_err(dev, "failed to get %s\n", LTQ_SPI_TX_IRQ_NAME);
                return -ENXIO;
        }

        err_irq = platform_get_irq_byname(pdev, LTQ_SPI_ERR_IRQ_NAME);
        if (err_irq < 0) {
                dev_err(dev, "failed to get %s\n", LTQ_SPI_ERR_IRQ_NAME);
                return -ENXIO;
        }

        master = spi_alloc_master(dev, sizeof(struct lantiq_ssc_spi));
        if (!master)
                return -ENOMEM;

        spi = spi_master_get_devdata(master);
        spi->master = master;
        spi->dev = dev;
        spi->hwcfg = hwcfg;
        platform_set_drvdata(pdev, spi);

        spi->regbase = devm_ioremap_resource(dev, res);
        if (IS_ERR(spi->regbase)) {
                err = PTR_ERR(spi->regbase);
                goto err_master_put;
        }

        err = devm_request_irq(dev, rx_irq, lantiq_ssc_xmit_interrupt,
                               0, LTQ_SPI_RX_IRQ_NAME, spi);
        if (err)
                goto err_master_put;

        err = devm_request_irq(dev, tx_irq, lantiq_ssc_xmit_interrupt,
                               0, LTQ_SPI_TX_IRQ_NAME, spi);
        if (err)
                goto err_master_put;

        err = devm_request_irq(dev, err_irq, lantiq_ssc_err_interrupt,
                               0, LTQ_SPI_ERR_IRQ_NAME, spi);
        if (err)
                goto err_master_put;

        spi->spi_clk = devm_clk_get(dev, "gate");
        if (IS_ERR(spi->spi_clk)) {
                err = PTR_ERR(spi->spi_clk);
                goto err_master_put;
        }
        err = clk_prepare_enable(spi->spi_clk);
        if (err)
                goto err_master_put;

        /*
         * Use the old clk_get_fpi() function on Lantiq platform, till it
         * supports common clk.
         */
#if defined(CONFIG_LANTIQ) && !defined(CONFIG_COMMON_CLK)
        spi->fpi_clk = clk_get_fpi();
#else
        spi->fpi_clk = clk_get(dev, "freq");
#endif
        if (IS_ERR(spi->fpi_clk)) {
                err = PTR_ERR(spi->fpi_clk);
                goto err_clk_disable;
        }

        num_cs = 8;
        of_property_read_u32(pdev->dev.of_node, "num-cs", &num_cs);

        spi->base_cs = 1;
        of_property_read_u32(pdev->dev.of_node, "base-cs", &spi->base_cs);

        spin_lock_init(&spi->lock);
        spi->bits_per_word = 8;
        spi->speed_hz = 0;

        master->dev.of_node = pdev->dev.of_node;
        master->num_chipselect = num_cs;
        master->setup = lantiq_ssc_setup;
        master->set_cs = lantiq_ssc_set_cs;
        master->handle_err = lantiq_ssc_handle_err;
        master->prepare_message = lantiq_ssc_prepare_message;
        master->unprepare_message = lantiq_ssc_unprepare_message;
        master->transfer_one = lantiq_ssc_transfer_one;
        master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_LSB_FIRST | SPI_CS_HIGH |
                                SPI_LOOP;
        master->bits_per_word_mask = SPI_BPW_RANGE_MASK(2, 8) |
                                     SPI_BPW_MASK(16) | SPI_BPW_MASK(32);

        spi->wq = alloc_ordered_workqueue(dev_name(dev), 0);
        if (!spi->wq) {
                err = -ENOMEM;
                goto err_clk_put;
        }
        INIT_WORK(&spi->work, lantiq_ssc_bussy_work);

        id = lantiq_ssc_readl(spi, LTQ_SPI_ID);
        spi->tx_fifo_size = (id & LTQ_SPI_ID_TXFS_M) >> LTQ_SPI_ID_TXFS_S;
        spi->rx_fifo_size = (id & LTQ_SPI_ID_RXFS_M) >> LTQ_SPI_ID_RXFS_S;
        supports_dma = (id & LTQ_SPI_ID_CFG_M) >> LTQ_SPI_ID_CFG_S;
        revision = id & LTQ_SPI_ID_REV_M;

        lantiq_ssc_hw_init(spi);

        dev_info(dev,
                "Lantiq SSC SPI controller (Rev %i, TXFS %u, RXFS %u, DMA %u)\n",
                revision, spi->tx_fifo_size, spi->rx_fifo_size, supports_dma);

        err = devm_spi_register_master(dev, master);
        if (err) {
                dev_err(dev, "failed to register spi_master\n");
                goto err_wq_destroy;
        }

        return 0;

err_wq_destroy:
        destroy_workqueue(spi->wq);
err_clk_put:
        clk_put(spi->fpi_clk);
err_clk_disable:
        clk_disable_unprepare(spi->spi_clk);
err_master_put:
        spi_master_put(master);

        return err;
}

static int lantiq_ssc_remove(struct platform_device *pdev)
{
        struct lantiq_ssc_spi *spi = platform_get_drvdata(pdev);

        lantiq_ssc_writel(spi, 0, LTQ_SPI_IRNEN);
        lantiq_ssc_writel(spi, 0, LTQ_SPI_CLC);
        rx_fifo_flush(spi);
        tx_fifo_flush(spi);
        hw_enter_config_mode(spi);

        destroy_workqueue(spi->wq);
        clk_disable_unprepare(spi->spi_clk);
        clk_put(spi->fpi_clk);

        return 0;
}

static struct platform_driver lantiq_ssc_driver = {
        .probe = lantiq_ssc_probe,
        .remove = lantiq_ssc_remove,
        .driver = {
                .name = "spi-lantiq-ssc",
                .of_match_table = lantiq_ssc_match,
        },
};
module_platform_driver(lantiq_ssc_driver);

MODULE_DESCRIPTION("Lantiq SSC SPI controller driver");
MODULE_AUTHOR("Daniel Schwierzeck <daniel.schwierzeck@gmail.com>");
MODULE_AUTHOR("Hauke Mehrtens <hauke@hauke-m.de>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:spi-lantiq-ssc");