eCryptfs: NULL pointer dereference in ecryptfs_send_miscdev()

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / drivers / spi / au1550_spi.c

/*
 * au1550_spi.c - au1550 psc spi controller driver
 * may work also with au1200, au1210, au1250
 * will not work on au1000, au1100 and au1500 (no full spi controller there)
 *
 * Copyright (c) 2006 ATRON electronic GmbH
 * Author: Jan Nikitenko <jan.nikitenko@gmail.com>
 *
 * 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/init.h>
#include <linux/interrupt.h>
#include <linux/errno.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/resource.h>
#include <linux/spi/spi.h>
#include <linux/spi/spi_bitbang.h>
#include <linux/dma-mapping.h>
#include <linux/completion.h>
#include <asm/mach-au1x00/au1000.h>
#include <asm/mach-au1x00/au1xxx_psc.h>
#include <asm/mach-au1x00/au1xxx_dbdma.h>

#include <asm/mach-au1x00/au1550_spi.h>

static unsigned usedma = 1;
module_param(usedma, uint, 0644);

/*
#define AU1550_SPI_DEBUG_LOOPBACK
*/


#define AU1550_SPI_DBDMA_DESCRIPTORS 1
#define AU1550_SPI_DMA_RXTMP_MINSIZE 2048U

struct au1550_spi {
        struct spi_bitbang bitbang;

        volatile psc_spi_t __iomem *regs;
        int irq;
        unsigned freq_max;
        unsigned freq_min;

        unsigned len;
        unsigned tx_count;
        unsigned rx_count;
        const u8 *tx;
        u8 *rx;

        void (*rx_word)(struct au1550_spi *hw);
        void (*tx_word)(struct au1550_spi *hw);
        int (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);
        irqreturn_t (*irq_callback)(struct au1550_spi *hw);

        struct completion master_done;

        unsigned usedma;
        u32 dma_tx_id;
        u32 dma_rx_id;
        u32 dma_tx_ch;
        u32 dma_rx_ch;

        u8 *dma_rx_tmpbuf;
        unsigned dma_rx_tmpbuf_size;
        u32 dma_rx_tmpbuf_addr;

        struct spi_master *master;
        struct device *dev;
        struct au1550_spi_info *pdata;
        struct resource *ioarea;
};


/* we use an 8-bit memory device for dma transfers to/from spi fifo */
static dbdev_tab_t au1550_spi_mem_dbdev =
{
        .dev_id                 = DBDMA_MEM_CHAN,
        .dev_flags              = DEV_FLAGS_ANYUSE|DEV_FLAGS_SYNC,
        .dev_tsize              = 0,
        .dev_devwidth           = 8,
        .dev_physaddr           = 0x00000000,
        .dev_intlevel           = 0,
        .dev_intpolarity        = 0
};

static int ddma_memid;  /* id to above mem dma device */

static void au1550_spi_bits_handlers_set(struct au1550_spi *hw, int bpw);


/*
 *  compute BRG and DIV bits to setup spi clock based on main input clock rate
 *  that was specified in platform data structure
 *  according to au1550 datasheet:
 *    psc_tempclk = psc_mainclk / (2 << DIV)
 *    spiclk = psc_tempclk / (2 * (BRG + 1))
 *    BRG valid range is 4..63
 *    DIV valid range is 0..3
 */
static u32 au1550_spi_baudcfg(struct au1550_spi *hw, unsigned speed_hz)
{
        u32 mainclk_hz = hw->pdata->mainclk_hz;
        u32 div, brg;

        for (div = 0; div < 4; div++) {
                brg = mainclk_hz / speed_hz / (4 << div);
                /* now we have BRG+1 in brg, so count with that */
                if (brg < (4 + 1)) {
                        brg = (4 + 1);  /* speed_hz too big */
                        break;          /* set lowest brg (div is == 0) */
                }
                if (brg <= (63 + 1))
                        break;          /* we have valid brg and div */
        }
        if (div == 4) {
                div = 3;                /* speed_hz too small */
                brg = (63 + 1);         /* set highest brg and div */
        }
        brg--;
        return PSC_SPICFG_SET_BAUD(brg) | PSC_SPICFG_SET_DIV(div);
}

static inline void au1550_spi_mask_ack_all(struct au1550_spi *hw)
{
        hw->regs->psc_spimsk =
                  PSC_SPIMSK_MM | PSC_SPIMSK_RR | PSC_SPIMSK_RO
                | PSC_SPIMSK_RU | PSC_SPIMSK_TR | PSC_SPIMSK_TO
                | PSC_SPIMSK_TU | PSC_SPIMSK_SD | PSC_SPIMSK_MD;
        au_sync();

        hw->regs->psc_spievent =
                  PSC_SPIEVNT_MM | PSC_SPIEVNT_RR | PSC_SPIEVNT_RO
                | PSC_SPIEVNT_RU | PSC_SPIEVNT_TR | PSC_SPIEVNT_TO
                | PSC_SPIEVNT_TU | PSC_SPIEVNT_SD | PSC_SPIEVNT_MD;
        au_sync();
}

static void au1550_spi_reset_fifos(struct au1550_spi *hw)
{
        u32 pcr;

        hw->regs->psc_spipcr = PSC_SPIPCR_RC | PSC_SPIPCR_TC;
        au_sync();
        do {
                pcr = hw->regs->psc_spipcr;
                au_sync();
        } while (pcr != 0);
}

/*
 * dma transfers are used for the most common spi word size of 8-bits
 * we cannot easily change already set up dma channels' width, so if we wanted
 * dma support for more than 8-bit words (up to 24 bits), we would need to
 * setup dma channels from scratch on each spi transfer, based on bits_per_word
 * instead we have pre set up 8 bit dma channels supporting spi 4 to 8 bits
 * transfers, and 9 to 24 bits spi transfers will be done in pio irq based mode
 * callbacks to handle dma or pio are set up in au1550_spi_bits_handlers_set()
 */
static void au1550_spi_chipsel(struct spi_device *spi, int value)
{
        struct au1550_spi *hw = spi_master_get_devdata(spi->master);
        unsigned cspol = spi->mode & SPI_CS_HIGH ? 1 : 0;
        u32 cfg, stat;

        switch (value) {
        case BITBANG_CS_INACTIVE:
                if (hw->pdata->deactivate_cs)
                        hw->pdata->deactivate_cs(hw->pdata, spi->chip_select,
                                        cspol);
                break;

        case BITBANG_CS_ACTIVE:
                au1550_spi_bits_handlers_set(hw, spi->bits_per_word);

                cfg = hw->regs->psc_spicfg;
                au_sync();
                hw->regs->psc_spicfg = cfg & ~PSC_SPICFG_DE_ENABLE;
                au_sync();

                if (spi->mode & SPI_CPOL)
                        cfg |= PSC_SPICFG_BI;
                else
                        cfg &= ~PSC_SPICFG_BI;
                if (spi->mode & SPI_CPHA)
                        cfg &= ~PSC_SPICFG_CDE;
                else
                        cfg |= PSC_SPICFG_CDE;

                if (spi->mode & SPI_LSB_FIRST)
                        cfg |= PSC_SPICFG_MLF;
                else
                        cfg &= ~PSC_SPICFG_MLF;

                if (hw->usedma && spi->bits_per_word <= 8)
                        cfg &= ~PSC_SPICFG_DD_DISABLE;
                else
                        cfg |= PSC_SPICFG_DD_DISABLE;
                cfg = PSC_SPICFG_CLR_LEN(cfg);
                cfg |= PSC_SPICFG_SET_LEN(spi->bits_per_word);

                cfg = PSC_SPICFG_CLR_BAUD(cfg);
                cfg &= ~PSC_SPICFG_SET_DIV(3);
                cfg |= au1550_spi_baudcfg(hw, spi->max_speed_hz);

                hw->regs->psc_spicfg = cfg | PSC_SPICFG_DE_ENABLE;
                au_sync();
                do {
                        stat = hw->regs->psc_spistat;
                        au_sync();
                } while ((stat & PSC_SPISTAT_DR) == 0);

                if (hw->pdata->activate_cs)
                        hw->pdata->activate_cs(hw->pdata, spi->chip_select,
                                        cspol);
                break;
        }
}

static int au1550_spi_setupxfer(struct spi_device *spi, struct spi_transfer *t)
{
        struct au1550_spi *hw = spi_master_get_devdata(spi->master);
        unsigned bpw, hz;
        u32 cfg, stat;

        bpw = t ? t->bits_per_word : spi->bits_per_word;
        hz = t ? t->speed_hz : spi->max_speed_hz;

        if (bpw < 4 || bpw > 24) {
                dev_err(&spi->dev, "setupxfer: invalid bits_per_word=%d\n",
                        bpw);
                return -EINVAL;
        }
        if (hz > spi->max_speed_hz || hz > hw->freq_max || hz < hw->freq_min) {
                dev_err(&spi->dev, "setupxfer: clock rate=%d out of range\n",
                        hz);
                return -EINVAL;
        }

        au1550_spi_bits_handlers_set(hw, spi->bits_per_word);

        cfg = hw->regs->psc_spicfg;
        au_sync();
        hw->regs->psc_spicfg = cfg & ~PSC_SPICFG_DE_ENABLE;
        au_sync();

        if (hw->usedma && bpw <= 8)
                cfg &= ~PSC_SPICFG_DD_DISABLE;
        else
                cfg |= PSC_SPICFG_DD_DISABLE;
        cfg = PSC_SPICFG_CLR_LEN(cfg);
        cfg |= PSC_SPICFG_SET_LEN(bpw);

        cfg = PSC_SPICFG_CLR_BAUD(cfg);
        cfg &= ~PSC_SPICFG_SET_DIV(3);
        cfg |= au1550_spi_baudcfg(hw, hz);

        hw->regs->psc_spicfg = cfg;
        au_sync();

        if (cfg & PSC_SPICFG_DE_ENABLE) {
                do {
                        stat = hw->regs->psc_spistat;
                        au_sync();
                } while ((stat & PSC_SPISTAT_DR) == 0);
        }

        au1550_spi_reset_fifos(hw);
        au1550_spi_mask_ack_all(hw);
        return 0;
}

/* the spi->mode bits understood by this driver: */
#define MODEBITS (SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_LSB_FIRST)

static int au1550_spi_setup(struct spi_device *spi)
{
        struct au1550_spi *hw = spi_master_get_devdata(spi->master);

        if (spi->bits_per_word == 0)
                spi->bits_per_word = 8;
        if (spi->bits_per_word < 4 || spi->bits_per_word > 24) {
                dev_err(&spi->dev, "setup: invalid bits_per_word=%d\n",
                        spi->bits_per_word);
                return -EINVAL;
        }

        if (spi->mode & ~MODEBITS) {
                dev_dbg(&spi->dev, "setup: unsupported mode bits %x\n",
                        spi->mode & ~MODEBITS);
                return -EINVAL;
        }

        if (spi->max_speed_hz == 0)
                spi->max_speed_hz = hw->freq_max;
        if (spi->max_speed_hz > hw->freq_max
                        || spi->max_speed_hz < hw->freq_min)
                return -EINVAL;
        /*
         * NOTE: cannot change speed and other hw settings immediately,
         *       otherwise sharing of spi bus is not possible,
         *       so do not call setupxfer(spi, NULL) here
         */
        return 0;
}

/*
 * for dma spi transfers, we have to setup rx channel, otherwise there is
 * no reliable way how to recognize that spi transfer is done
 * dma complete callbacks are called before real spi transfer is finished
 * and if only tx dma channel is set up (and rx fifo overflow event masked)
 * spi master done event irq is not generated unless rx fifo is empty (emptied)
 * so we need rx tmp buffer to use for rx dma if user does not provide one
 */
static int au1550_spi_dma_rxtmp_alloc(struct au1550_spi *hw, unsigned size)
{
        hw->dma_rx_tmpbuf = kmalloc(size, GFP_KERNEL);
        if (!hw->dma_rx_tmpbuf)
                return -ENOMEM;
        hw->dma_rx_tmpbuf_size = size;
        hw->dma_rx_tmpbuf_addr = dma_map_single(hw->dev, hw->dma_rx_tmpbuf,
                        size, DMA_FROM_DEVICE);
        if (dma_mapping_error(hw->dev, hw->dma_rx_tmpbuf_addr)) {
                kfree(hw->dma_rx_tmpbuf);
                hw->dma_rx_tmpbuf = 0;
                hw->dma_rx_tmpbuf_size = 0;
                return -EFAULT;
        }
        return 0;
}

static void au1550_spi_dma_rxtmp_free(struct au1550_spi *hw)
{
        dma_unmap_single(hw->dev, hw->dma_rx_tmpbuf_addr,
                        hw->dma_rx_tmpbuf_size, DMA_FROM_DEVICE);
        kfree(hw->dma_rx_tmpbuf);
        hw->dma_rx_tmpbuf = 0;
        hw->dma_rx_tmpbuf_size = 0;
}

static int au1550_spi_dma_txrxb(struct spi_device *spi, struct spi_transfer *t)
{
        struct au1550_spi *hw = spi_master_get_devdata(spi->master);
        dma_addr_t dma_tx_addr;
        dma_addr_t dma_rx_addr;
        u32 res;

        hw->len = t->len;
        hw->tx_count = 0;
        hw->rx_count = 0;

        hw->tx = t->tx_buf;
        hw->rx = t->rx_buf;
        dma_tx_addr = t->tx_dma;
        dma_rx_addr = t->rx_dma;

        /*
         * check if buffers are already dma mapped, map them otherwise:
         * - first map the TX buffer, so cache data gets written to memory
         * - then map the RX buffer, so that cache entries (with
         *   soon-to-be-stale data) get removed
         * use rx buffer in place of tx if tx buffer was not provided
         * use temp rx buffer (preallocated or realloc to fit) for rx dma
         */
        if (t->tx_buf) {
                if (t->tx_dma == 0) {   /* if DMA_ADDR_INVALID, map it */
                        dma_tx_addr = dma_map_single(hw->dev,
                                        (void *)t->tx_buf,
                                        t->len, DMA_TO_DEVICE);
                        if (dma_mapping_error(hw->dev, dma_tx_addr))
                                dev_err(hw->dev, "tx dma map error\n");
                }
        }

        if (t->rx_buf) {
                if (t->rx_dma == 0) {   /* if DMA_ADDR_INVALID, map it */
                        dma_rx_addr = dma_map_single(hw->dev,
                                        (void *)t->rx_buf,
                                        t->len, DMA_FROM_DEVICE);
                        if (dma_mapping_error(hw->dev, dma_rx_addr))
                                dev_err(hw->dev, "rx dma map error\n");
                }
        } else {
                if (t->len > hw->dma_rx_tmpbuf_size) {
                        int ret;

                        au1550_spi_dma_rxtmp_free(hw);
                        ret = au1550_spi_dma_rxtmp_alloc(hw, max(t->len,
                                        AU1550_SPI_DMA_RXTMP_MINSIZE));
                        if (ret < 0)
                                return ret;
                }
                hw->rx = hw->dma_rx_tmpbuf;
                dma_rx_addr = hw->dma_rx_tmpbuf_addr;
                dma_sync_single_for_device(hw->dev, dma_rx_addr,
                        t->len, DMA_FROM_DEVICE);
        }

        if (!t->tx_buf) {
                dma_sync_single_for_device(hw->dev, dma_rx_addr,
                                t->len, DMA_BIDIRECTIONAL);
                hw->tx = hw->rx;
        }

        /* put buffers on the ring */
        res = au1xxx_dbdma_put_dest(hw->dma_rx_ch, hw->rx, t->len);
        if (!res)
                dev_err(hw->dev, "rx dma put dest error\n");

        res = au1xxx_dbdma_put_source(hw->dma_tx_ch, (void *)hw->tx, t->len);
        if (!res)
                dev_err(hw->dev, "tx dma put source error\n");

        au1xxx_dbdma_start(hw->dma_rx_ch);
        au1xxx_dbdma_start(hw->dma_tx_ch);

        /* by default enable nearly all events interrupt */
        hw->regs->psc_spimsk = PSC_SPIMSK_SD;
        au_sync();

        /* start the transfer */
        hw->regs->psc_spipcr = PSC_SPIPCR_MS;
        au_sync();

        wait_for_completion(&hw->master_done);

        au1xxx_dbdma_stop(hw->dma_tx_ch);
        au1xxx_dbdma_stop(hw->dma_rx_ch);

        if (!t->rx_buf) {
                /* using the temporal preallocated and premapped buffer */
                dma_sync_single_for_cpu(hw->dev, dma_rx_addr, t->len,
                        DMA_FROM_DEVICE);
        }
        /* unmap buffers if mapped above */
        if (t->rx_buf && t->rx_dma == 0 )
                dma_unmap_single(hw->dev, dma_rx_addr, t->len,
                        DMA_FROM_DEVICE);
        if (t->tx_buf && t->tx_dma == 0 )
                dma_unmap_single(hw->dev, dma_tx_addr, t->len,
                        DMA_TO_DEVICE);

        return hw->rx_count < hw->tx_count ? hw->rx_count : hw->tx_count;
}

static irqreturn_t au1550_spi_dma_irq_callback(struct au1550_spi *hw)
{
        u32 stat, evnt;

        stat = hw->regs->psc_spistat;
        evnt = hw->regs->psc_spievent;
        au_sync();
        if ((stat & PSC_SPISTAT_DI) == 0) {
                dev_err(hw->dev, "Unexpected IRQ!\n");
                return IRQ_NONE;
        }

        if ((evnt & (PSC_SPIEVNT_MM | PSC_SPIEVNT_RO
                                | PSC_SPIEVNT_RU | PSC_SPIEVNT_TO
                                | PSC_SPIEVNT_TU | PSC_SPIEVNT_SD))
                        != 0) {
                /*
                 * due to an spi error we consider transfer as done,
                 * so mask all events until before next transfer start
                 * and stop the possibly running dma immediatelly
                 */
                au1550_spi_mask_ack_all(hw);
                au1xxx_dbdma_stop(hw->dma_rx_ch);
                au1xxx_dbdma_stop(hw->dma_tx_ch);

                /* get number of transfered bytes */
                hw->rx_count = hw->len - au1xxx_get_dma_residue(hw->dma_rx_ch);
                hw->tx_count = hw->len - au1xxx_get_dma_residue(hw->dma_tx_ch);

                au1xxx_dbdma_reset(hw->dma_rx_ch);
                au1xxx_dbdma_reset(hw->dma_tx_ch);
                au1550_spi_reset_fifos(hw);

                if (evnt == PSC_SPIEVNT_RO)
                        dev_err(hw->dev,
                                "dma transfer: receive FIFO overflow!\n");
                else
                        dev_err(hw->dev,
                                "dma transfer: unexpected SPI error "
                                "(event=0x%x stat=0x%x)!\n", evnt, stat);

                complete(&hw->master_done);
                return IRQ_HANDLED;
        }

        if ((evnt & PSC_SPIEVNT_MD) != 0) {
                /* transfer completed successfully */
                au1550_spi_mask_ack_all(hw);
                hw->rx_count = hw->len;
                hw->tx_count = hw->len;
                complete(&hw->master_done);
        }
        return IRQ_HANDLED;
}


/* routines to handle different word sizes in pio mode */
#define AU1550_SPI_RX_WORD(size, mask)                                  \
static void au1550_spi_rx_word_##size(struct au1550_spi *hw)            \
{                                                                       \
        u32 fifoword = hw->regs->psc_spitxrx & (u32)(mask);             \
        au_sync();                                                      \
        if (hw->rx) {                                                   \
                *(u##size *)hw->rx = (u##size)fifoword;                 \
                hw->rx += (size) / 8;                                   \
        }                                                               \
        hw->rx_count += (size) / 8;                                     \
}

#define AU1550_SPI_TX_WORD(size, mask)                                  \
static void au1550_spi_tx_word_##size(struct au1550_spi *hw)            \
{                                                                       \
        u32 fifoword = 0;                                               \
        if (hw->tx) {                                                   \
                fifoword = *(u##size *)hw->tx & (u32)(mask);            \
                hw->tx += (size) / 8;                                   \
        }                                                               \
        hw->tx_count += (size) / 8;                                     \
        if (hw->tx_count >= hw->len)                                    \
                fifoword |= PSC_SPITXRX_LC;                             \
        hw->regs->psc_spitxrx = fifoword;                               \
        au_sync();                                                      \
}

AU1550_SPI_RX_WORD(8,0xff)
AU1550_SPI_RX_WORD(16,0xffff)
AU1550_SPI_RX_WORD(32,0xffffff)
AU1550_SPI_TX_WORD(8,0xff)
AU1550_SPI_TX_WORD(16,0xffff)
AU1550_SPI_TX_WORD(32,0xffffff)

static int au1550_spi_pio_txrxb(struct spi_device *spi, struct spi_transfer *t)
{
        u32 stat, mask;
        struct au1550_spi *hw = spi_master_get_devdata(spi->master);

        hw->tx = t->tx_buf;
        hw->rx = t->rx_buf;
        hw->len = t->len;
        hw->tx_count = 0;
        hw->rx_count = 0;

        /* by default enable nearly all events after filling tx fifo */
        mask = PSC_SPIMSK_SD;

        /* fill the transmit FIFO */
        while (hw->tx_count < hw->len) {

                hw->tx_word(hw);

                if (hw->tx_count >= hw->len) {
                        /* mask tx fifo request interrupt as we are done */
                        mask |= PSC_SPIMSK_TR;
                }

                stat = hw->regs->psc_spistat;
                au_sync();
                if (stat & PSC_SPISTAT_TF)
                        break;
        }

        /* enable event interrupts */
        hw->regs->psc_spimsk = mask;
        au_sync();

        /* start the transfer */
        hw->regs->psc_spipcr = PSC_SPIPCR_MS;
        au_sync();

        wait_for_completion(&hw->master_done);

        return hw->rx_count < hw->tx_count ? hw->rx_count : hw->tx_count;
}

static irqreturn_t au1550_spi_pio_irq_callback(struct au1550_spi *hw)
{
        int busy;
        u32 stat, evnt;

        stat = hw->regs->psc_spistat;
        evnt = hw->regs->psc_spievent;
        au_sync();
        if ((stat & PSC_SPISTAT_DI) == 0) {
                dev_err(hw->dev, "Unexpected IRQ!\n");
                return IRQ_NONE;
        }

        if ((evnt & (PSC_SPIEVNT_MM | PSC_SPIEVNT_RO
                                | PSC_SPIEVNT_RU | PSC_SPIEVNT_TO
                                | PSC_SPIEVNT_SD))
                        != 0) {
                /*
                 * due to an error we consider transfer as done,
                 * so mask all events until before next transfer start
                 */
                au1550_spi_mask_ack_all(hw);
                au1550_spi_reset_fifos(hw);
                dev_err(hw->dev,
                        "pio transfer: unexpected SPI error "
                        "(event=0x%x stat=0x%x)!\n", evnt, stat);
                complete(&hw->master_done);
                return IRQ_HANDLED;
        }

        /*
         * while there is something to read from rx fifo
         * or there is a space to write to tx fifo:
         */
        do {
                busy = 0;
                stat = hw->regs->psc_spistat;
                au_sync();

                /*
                 * Take care to not let the Rx FIFO overflow.
                 *
                 * We only write a byte if we have read one at least. Initially,
                 * the write fifo is full, so we should read from the read fifo
                 * first.
                 * In case we miss a word from the read fifo, we should get a
                 * RO event and should back out.
                 */
                if (!(stat & PSC_SPISTAT_RE) && hw->rx_count < hw->len) {
                        hw->rx_word(hw);
                        busy = 1;

                        if (!(stat & PSC_SPISTAT_TF) && hw->tx_count < hw->len)
                                hw->tx_word(hw);
                }
        } while (busy);

        hw->regs->psc_spievent = PSC_SPIEVNT_RR | PSC_SPIEVNT_TR;
        au_sync();

        /*
         * Restart the SPI transmission in case of a transmit underflow.
         * This seems to work despite the notes in the Au1550 data book
         * of Figure 8-4 with flowchart for SPI master operation:
         *
         * """Note 1: An XFR Error Interrupt occurs, unless masked,
         * for any of the following events: Tx FIFO Underflow,
         * Rx FIFO Overflow, or Multiple-master Error
         *    Note 2: In case of a Tx Underflow Error, all zeroes are
         * transmitted."""
         *
         * By simply restarting the spi transfer on Tx Underflow Error,
         * we assume that spi transfer was paused instead of zeroes
         * transmittion mentioned in the Note 2 of Au1550 data book.
         */
        if (evnt & PSC_SPIEVNT_TU) {
                hw->regs->psc_spievent = PSC_SPIEVNT_TU | PSC_SPIEVNT_MD;
                au_sync();
                hw->regs->psc_spipcr = PSC_SPIPCR_MS;
                au_sync();
        }

        if (hw->rx_count >= hw->len) {
                /* transfer completed successfully */
                au1550_spi_mask_ack_all(hw);
                complete(&hw->master_done);
        }
        return IRQ_HANDLED;
}

static int au1550_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
{
        struct au1550_spi *hw = spi_master_get_devdata(spi->master);
        return hw->txrx_bufs(spi, t);
}

static irqreturn_t au1550_spi_irq(int irq, void *dev)
{
        struct au1550_spi *hw = dev;
        return hw->irq_callback(hw);
}

static void au1550_spi_bits_handlers_set(struct au1550_spi *hw, int bpw)
{
        if (bpw <= 8) {
                if (hw->usedma) {
                        hw->txrx_bufs = &au1550_spi_dma_txrxb;
                        hw->irq_callback = &au1550_spi_dma_irq_callback;
                } else {
                        hw->rx_word = &au1550_spi_rx_word_8;
                        hw->tx_word = &au1550_spi_tx_word_8;
                        hw->txrx_bufs = &au1550_spi_pio_txrxb;
                        hw->irq_callback = &au1550_spi_pio_irq_callback;
                }
        } else if (bpw <= 16) {
                hw->rx_word = &au1550_spi_rx_word_16;
                hw->tx_word = &au1550_spi_tx_word_16;
                hw->txrx_bufs = &au1550_spi_pio_txrxb;
                hw->irq_callback = &au1550_spi_pio_irq_callback;
        } else {
                hw->rx_word = &au1550_spi_rx_word_32;
                hw->tx_word = &au1550_spi_tx_word_32;
                hw->txrx_bufs = &au1550_spi_pio_txrxb;
                hw->irq_callback = &au1550_spi_pio_irq_callback;
        }
}

static void __init au1550_spi_setup_psc_as_spi(struct au1550_spi *hw)
{
        u32 stat, cfg;

        /* set up the PSC for SPI mode */
        hw->regs->psc_ctrl = PSC_CTRL_DISABLE;
        au_sync();
        hw->regs->psc_sel = PSC_SEL_PS_SPIMODE;
        au_sync();

        hw->regs->psc_spicfg = 0;
        au_sync();

        hw->regs->psc_ctrl = PSC_CTRL_ENABLE;
        au_sync();

        do {
                stat = hw->regs->psc_spistat;
                au_sync();
        } while ((stat & PSC_SPISTAT_SR) == 0);


        cfg = hw->usedma ? 0 : PSC_SPICFG_DD_DISABLE;
        cfg |= PSC_SPICFG_SET_LEN(8);
        cfg |= PSC_SPICFG_RT_FIFO8 | PSC_SPICFG_TT_FIFO8;
        /* use minimal allowed brg and div values as initial setting: */
        cfg |= PSC_SPICFG_SET_BAUD(4) | PSC_SPICFG_SET_DIV(0);

#ifdef AU1550_SPI_DEBUG_LOOPBACK
        cfg |= PSC_SPICFG_LB;
#endif

        hw->regs->psc_spicfg = cfg;
        au_sync();

        au1550_spi_mask_ack_all(hw);

        hw->regs->psc_spicfg |= PSC_SPICFG_DE_ENABLE;
        au_sync();

        do {
                stat = hw->regs->psc_spistat;
                au_sync();
        } while ((stat & PSC_SPISTAT_DR) == 0);

        au1550_spi_reset_fifos(hw);
}


static int __init au1550_spi_probe(struct platform_device *pdev)
{
        struct au1550_spi *hw;
        struct spi_master *master;
        struct resource *r;
        int err = 0;

        master = spi_alloc_master(&pdev->dev, sizeof(struct au1550_spi));
        if (master == NULL) {
                dev_err(&pdev->dev, "No memory for spi_master\n");
                err = -ENOMEM;
                goto err_nomem;
        }

        hw = spi_master_get_devdata(master);

        hw->master = spi_master_get(master);
        hw->pdata = pdev->dev.platform_data;
        hw->dev = &pdev->dev;

        if (hw->pdata == NULL) {
                dev_err(&pdev->dev, "No platform data supplied\n");
                err = -ENOENT;
                goto err_no_pdata;
        }

        r = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
        if (!r) {
                dev_err(&pdev->dev, "no IRQ\n");
                err = -ENODEV;
                goto err_no_iores;
        }
        hw->irq = r->start;

        hw->usedma = 0;
        r = platform_get_resource(pdev, IORESOURCE_DMA, 0);
        if (r) {
                hw->dma_tx_id = r->start;
                r = platform_get_resource(pdev, IORESOURCE_DMA, 1);
                if (r) {
                        hw->dma_rx_id = r->start;
                        if (usedma && ddma_memid) {
                                if (pdev->dev.dma_mask == NULL)
                                        dev_warn(&pdev->dev, "no dma mask\n");
                                else
                                        hw->usedma = 1;
                        }
                }
        }

        r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (!r) {
                dev_err(&pdev->dev, "no mmio resource\n");
                err = -ENODEV;
                goto err_no_iores;
        }

        hw->ioarea = request_mem_region(r->start, sizeof(psc_spi_t),
                                        pdev->name);
        if (!hw->ioarea) {
                dev_err(&pdev->dev, "Cannot reserve iomem region\n");
                err = -ENXIO;
                goto err_no_iores;
        }

        hw->regs = (psc_spi_t __iomem *)ioremap(r->start, sizeof(psc_spi_t));
        if (!hw->regs) {
                dev_err(&pdev->dev, "cannot ioremap\n");
                err = -ENXIO;
                goto err_ioremap;
        }

        platform_set_drvdata(pdev, hw);

        init_completion(&hw->master_done);

        hw->bitbang.master = hw->master;
        hw->bitbang.setup_transfer = au1550_spi_setupxfer;
        hw->bitbang.chipselect = au1550_spi_chipsel;
        hw->bitbang.master->setup = au1550_spi_setup;
        hw->bitbang.txrx_bufs = au1550_spi_txrx_bufs;

        if (hw->usedma) {
                hw->dma_tx_ch = au1xxx_dbdma_chan_alloc(ddma_memid,
                        hw->dma_tx_id, NULL, (void *)hw);
                if (hw->dma_tx_ch == 0) {
                        dev_err(&pdev->dev,
                                "Cannot allocate tx dma channel\n");
                        err = -ENXIO;
                        goto err_no_txdma;
                }
                au1xxx_dbdma_set_devwidth(hw->dma_tx_ch, 8);
                if (au1xxx_dbdma_ring_alloc(hw->dma_tx_ch,
                        AU1550_SPI_DBDMA_DESCRIPTORS) == 0) {
                        dev_err(&pdev->dev,
                                "Cannot allocate tx dma descriptors\n");
                        err = -ENXIO;
                        goto err_no_txdma_descr;
                }


                hw->dma_rx_ch = au1xxx_dbdma_chan_alloc(hw->dma_rx_id,
                        ddma_memid, NULL, (void *)hw);
                if (hw->dma_rx_ch == 0) {
                        dev_err(&pdev->dev,
                                "Cannot allocate rx dma channel\n");
                        err = -ENXIO;
                        goto err_no_rxdma;
                }
                au1xxx_dbdma_set_devwidth(hw->dma_rx_ch, 8);
                if (au1xxx_dbdma_ring_alloc(hw->dma_rx_ch,
                        AU1550_SPI_DBDMA_DESCRIPTORS) == 0) {
                        dev_err(&pdev->dev,
                                "Cannot allocate rx dma descriptors\n");
                        err = -ENXIO;
                        goto err_no_rxdma_descr;
                }

                err = au1550_spi_dma_rxtmp_alloc(hw,
                        AU1550_SPI_DMA_RXTMP_MINSIZE);
                if (err < 0) {
                        dev_err(&pdev->dev,
                                "Cannot allocate initial rx dma tmp buffer\n");
                        goto err_dma_rxtmp_alloc;
                }
        }

        au1550_spi_bits_handlers_set(hw, 8);

        err = request_irq(hw->irq, au1550_spi_irq, 0, pdev->name, hw);
        if (err) {
                dev_err(&pdev->dev, "Cannot claim IRQ\n");
                goto err_no_irq;
        }

        master->bus_num = pdev->id;
        master->num_chipselect = hw->pdata->num_chipselect;

        /*
         *  precompute valid range for spi freq - from au1550 datasheet:
         *    psc_tempclk = psc_mainclk / (2 << DIV)
         *    spiclk = psc_tempclk / (2 * (BRG + 1))
         *    BRG valid range is 4..63
         *    DIV valid range is 0..3
         *  round the min and max frequencies to values that would still
         *  produce valid brg and div
         */
        {
                int min_div = (2 << 0) * (2 * (4 + 1));
                int max_div = (2 << 3) * (2 * (63 + 1));
                hw->freq_max = hw->pdata->mainclk_hz / min_div;
                hw->freq_min = hw->pdata->mainclk_hz / (max_div + 1) + 1;
        }

        au1550_spi_setup_psc_as_spi(hw);

        err = spi_bitbang_start(&hw->bitbang);
        if (err) {
                dev_err(&pdev->dev, "Failed to register SPI master\n");
                goto err_register;
        }

        dev_info(&pdev->dev,
                "spi master registered: bus_num=%d num_chipselect=%d\n",
                master->bus_num, master->num_chipselect);

        return 0;

err_register:
        free_irq(hw->irq, hw);

err_no_irq:
        au1550_spi_dma_rxtmp_free(hw);

err_dma_rxtmp_alloc:
err_no_rxdma_descr:
        if (hw->usedma)
                au1xxx_dbdma_chan_free(hw->dma_rx_ch);

err_no_rxdma:
err_no_txdma_descr:
        if (hw->usedma)
                au1xxx_dbdma_chan_free(hw->dma_tx_ch);

err_no_txdma:
        iounmap((void __iomem *)hw->regs);

err_ioremap:
        release_resource(hw->ioarea);
        kfree(hw->ioarea);

err_no_iores:
err_no_pdata:
        spi_master_put(hw->master);

err_nomem:
        return err;
}

static int __exit au1550_spi_remove(struct platform_device *pdev)
{
        struct au1550_spi *hw = platform_get_drvdata(pdev);

        dev_info(&pdev->dev, "spi master remove: bus_num=%d\n",
                hw->master->bus_num);

        spi_bitbang_stop(&hw->bitbang);
        free_irq(hw->irq, hw);
        iounmap((void __iomem *)hw->regs);
        release_resource(hw->ioarea);
        kfree(hw->ioarea);

        if (hw->usedma) {
                au1550_spi_dma_rxtmp_free(hw);
                au1xxx_dbdma_chan_free(hw->dma_rx_ch);
                au1xxx_dbdma_chan_free(hw->dma_tx_ch);
        }

        platform_set_drvdata(pdev, NULL);

        spi_master_put(hw->master);
        return 0;
}

/* work with hotplug and coldplug */
MODULE_ALIAS("platform:au1550-spi");

static struct platform_driver au1550_spi_drv = {
        .remove = __exit_p(au1550_spi_remove),
        .driver = {
                .name = "au1550-spi",
                .owner = THIS_MODULE,
        },
};

static int __init au1550_spi_init(void)
{
        /*
         * create memory device with 8 bits dev_devwidth
         * needed for proper byte ordering to spi fifo
         */
        if (usedma) {
                ddma_memid = au1xxx_ddma_add_device(&au1550_spi_mem_dbdev);
                if (!ddma_memid)
                        printk(KERN_ERR "au1550-spi: cannot add memory"
                                        "dbdma device\n");
        }
        return platform_driver_probe(&au1550_spi_drv, au1550_spi_probe);
}
module_init(au1550_spi_init);

static void __exit au1550_spi_exit(void)
{
        if (usedma && ddma_memid)
                au1xxx_ddma_del_device(ddma_memid);
        platform_driver_unregister(&au1550_spi_drv);
}
module_exit(au1550_spi_exit);

MODULE_DESCRIPTION("Au1550 PSC SPI Driver");
MODULE_AUTHOR("Jan Nikitenko <jan.nikitenko@gmail.com>");
MODULE_LICENSE("GPL");