Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[cris-mirror.git] / drivers / i2c / busses / i2c-at91.c

/*
 *  i2c Support for Atmel's AT91 Two-Wire Interface (TWI)
 *
 *  Copyright (C) 2011 Weinmann Medical GmbH
 *  Author: Nikolaus Voss <n.voss@weinmann.de>
 *
 *  Evolved from original work by:
 *  Copyright (C) 2004 Rick Bronson
 *  Converted to 2.6 by Andrew Victor <andrew@sanpeople.com>
 *
 *  Borrowed heavily from original work by:
 *  Copyright (C) 2000 Philip Edelbrock <phil@stimpy.netroedge.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.
 */

#include <linux/clk.h>
#include <linux/completion.h>
#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/err.h>
#include <linux/i2c.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/platform_data/dma-atmel.h>
#include <linux/pm_runtime.h>
#include <linux/pinctrl/consumer.h>

#define DEFAULT_TWI_CLK_HZ              100000          /* max 400 Kbits/s */
#define AT91_I2C_TIMEOUT        msecs_to_jiffies(100)   /* transfer timeout */
#define AT91_I2C_DMA_THRESHOLD  8                       /* enable DMA if transfer size is bigger than this threshold */
#define AUTOSUSPEND_TIMEOUT             2000
#define AT91_I2C_MAX_ALT_CMD_DATA_SIZE  256

/* AT91 TWI register definitions */
#define AT91_TWI_CR             0x0000  /* Control Register */
#define AT91_TWI_START          BIT(0)  /* Send a Start Condition */
#define AT91_TWI_STOP           BIT(1)  /* Send a Stop Condition */
#define AT91_TWI_MSEN           BIT(2)  /* Master Transfer Enable */
#define AT91_TWI_MSDIS          BIT(3)  /* Master Transfer Disable */
#define AT91_TWI_SVEN           BIT(4)  /* Slave Transfer Enable */
#define AT91_TWI_SVDIS          BIT(5)  /* Slave Transfer Disable */
#define AT91_TWI_QUICK          BIT(6)  /* SMBus quick command */
#define AT91_TWI_SWRST          BIT(7)  /* Software Reset */
#define AT91_TWI_ACMEN          BIT(16) /* Alternative Command Mode Enable */
#define AT91_TWI_ACMDIS         BIT(17) /* Alternative Command Mode Disable */
#define AT91_TWI_THRCLR         BIT(24) /* Transmit Holding Register Clear */
#define AT91_TWI_RHRCLR         BIT(25) /* Receive Holding Register Clear */
#define AT91_TWI_LOCKCLR        BIT(26) /* Lock Clear */
#define AT91_TWI_FIFOEN         BIT(28) /* FIFO Enable */
#define AT91_TWI_FIFODIS        BIT(29) /* FIFO Disable */

#define AT91_TWI_MMR            0x0004  /* Master Mode Register */
#define AT91_TWI_IADRSZ_1       0x0100  /* Internal Device Address Size */
#define AT91_TWI_MREAD          BIT(12) /* Master Read Direction */

#define AT91_TWI_IADR           0x000c  /* Internal Address Register */

#define AT91_TWI_CWGR           0x0010  /* Clock Waveform Generator Reg */
#define AT91_TWI_CWGR_HOLD_MAX  0x1f
#define AT91_TWI_CWGR_HOLD(x)   (((x) & AT91_TWI_CWGR_HOLD_MAX) << 24)

#define AT91_TWI_SR             0x0020  /* Status Register */
#define AT91_TWI_TXCOMP         BIT(0)  /* Transmission Complete */
#define AT91_TWI_RXRDY          BIT(1)  /* Receive Holding Register Ready */
#define AT91_TWI_TXRDY          BIT(2)  /* Transmit Holding Register Ready */
#define AT91_TWI_OVRE           BIT(6)  /* Overrun Error */
#define AT91_TWI_UNRE           BIT(7)  /* Underrun Error */
#define AT91_TWI_NACK           BIT(8)  /* Not Acknowledged */
#define AT91_TWI_LOCK           BIT(23) /* TWI Lock due to Frame Errors */

#define AT91_TWI_INT_MASK \
        (AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY | AT91_TWI_NACK)

#define AT91_TWI_IER            0x0024  /* Interrupt Enable Register */
#define AT91_TWI_IDR            0x0028  /* Interrupt Disable Register */
#define AT91_TWI_IMR            0x002c  /* Interrupt Mask Register */
#define AT91_TWI_RHR            0x0030  /* Receive Holding Register */
#define AT91_TWI_THR            0x0034  /* Transmit Holding Register */

#define AT91_TWI_ACR            0x0040  /* Alternative Command Register */
#define AT91_TWI_ACR_DATAL(len) ((len) & 0xff)
#define AT91_TWI_ACR_DIR        BIT(8)

#define AT91_TWI_FMR            0x0050  /* FIFO Mode Register */
#define AT91_TWI_FMR_TXRDYM(mode)       (((mode) & 0x3) << 0)
#define AT91_TWI_FMR_TXRDYM_MASK        (0x3 << 0)
#define AT91_TWI_FMR_RXRDYM(mode)       (((mode) & 0x3) << 4)
#define AT91_TWI_FMR_RXRDYM_MASK        (0x3 << 4)
#define AT91_TWI_ONE_DATA       0x0
#define AT91_TWI_TWO_DATA       0x1
#define AT91_TWI_FOUR_DATA      0x2

#define AT91_TWI_FLR            0x0054  /* FIFO Level Register */

#define AT91_TWI_FSR            0x0060  /* FIFO Status Register */
#define AT91_TWI_FIER           0x0064  /* FIFO Interrupt Enable Register */
#define AT91_TWI_FIDR           0x0068  /* FIFO Interrupt Disable Register */
#define AT91_TWI_FIMR           0x006c  /* FIFO Interrupt Mask Register */

#define AT91_TWI_VER            0x00fc  /* Version Register */

struct at91_twi_pdata {
        unsigned clk_max_div;
        unsigned clk_offset;
        bool has_unre_flag;
        bool has_alt_cmd;
        bool has_hold_field;
        struct at_dma_slave dma_slave;
};

struct at91_twi_dma {
        struct dma_chan *chan_rx;
        struct dma_chan *chan_tx;
        struct scatterlist sg[2];
        struct dma_async_tx_descriptor *data_desc;
        enum dma_data_direction direction;
        bool buf_mapped;
        bool xfer_in_progress;
};

struct at91_twi_dev {
        struct device *dev;
        void __iomem *base;
        struct completion cmd_complete;
        struct clk *clk;
        u8 *buf;
        size_t buf_len;
        struct i2c_msg *msg;
        int irq;
        unsigned imr;
        unsigned transfer_status;
        struct i2c_adapter adapter;
        unsigned twi_cwgr_reg;
        struct at91_twi_pdata *pdata;
        bool use_dma;
        bool use_alt_cmd;
        bool recv_len_abort;
        u32 fifo_size;
        struct at91_twi_dma dma;
};

static unsigned at91_twi_read(struct at91_twi_dev *dev, unsigned reg)
{
        return readl_relaxed(dev->base + reg);
}

static void at91_twi_write(struct at91_twi_dev *dev, unsigned reg, unsigned val)
{
        writel_relaxed(val, dev->base + reg);
}

static void at91_disable_twi_interrupts(struct at91_twi_dev *dev)
{
        at91_twi_write(dev, AT91_TWI_IDR, AT91_TWI_INT_MASK);
}

static void at91_twi_irq_save(struct at91_twi_dev *dev)
{
        dev->imr = at91_twi_read(dev, AT91_TWI_IMR) & AT91_TWI_INT_MASK;
        at91_disable_twi_interrupts(dev);
}

static void at91_twi_irq_restore(struct at91_twi_dev *dev)
{
        at91_twi_write(dev, AT91_TWI_IER, dev->imr);
}

static void at91_init_twi_bus(struct at91_twi_dev *dev)
{
        at91_disable_twi_interrupts(dev);
        at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SWRST);
        /* FIFO should be enabled immediately after the software reset */
        if (dev->fifo_size)
                at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_FIFOEN);
        at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_MSEN);
        at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SVDIS);
        at91_twi_write(dev, AT91_TWI_CWGR, dev->twi_cwgr_reg);
}

/*
 * Calculate symmetric clock as stated in datasheet:
 * twi_clk = F_MAIN / (2 * (cdiv * (1 << ckdiv) + offset))
 */
static void at91_calc_twi_clock(struct at91_twi_dev *dev, int twi_clk)
{
        int ckdiv, cdiv, div, hold = 0;
        struct at91_twi_pdata *pdata = dev->pdata;
        int offset = pdata->clk_offset;
        int max_ckdiv = pdata->clk_max_div;
        u32 twd_hold_time_ns = 0;

        div = max(0, (int)DIV_ROUND_UP(clk_get_rate(dev->clk),
                                       2 * twi_clk) - offset);
        ckdiv = fls(div >> 8);
        cdiv = div >> ckdiv;

        if (ckdiv > max_ckdiv) {
                dev_warn(dev->dev, "%d exceeds ckdiv max value which is %d.\n",
                         ckdiv, max_ckdiv);
                ckdiv = max_ckdiv;
                cdiv = 255;
        }

        if (pdata->has_hold_field) {
                of_property_read_u32(dev->dev->of_node, "i2c-sda-hold-time-ns",
                                     &twd_hold_time_ns);

                /*
                 * hold time = HOLD + 3 x T_peripheral_clock
                 * Use clk rate in kHz to prevent overflows when computing
                 * hold.
                 */
                hold = DIV_ROUND_UP(twd_hold_time_ns
                                    * (clk_get_rate(dev->clk) / 1000), 1000000);
                hold -= 3;
                if (hold < 0)
                        hold = 0;
                if (hold > AT91_TWI_CWGR_HOLD_MAX) {
                        dev_warn(dev->dev,
                                 "HOLD field set to its maximum value (%d instead of %d)\n",
                                 AT91_TWI_CWGR_HOLD_MAX, hold);
                        hold = AT91_TWI_CWGR_HOLD_MAX;
                }
        }

        dev->twi_cwgr_reg = (ckdiv << 16) | (cdiv << 8) | cdiv
                            | AT91_TWI_CWGR_HOLD(hold);

        dev_dbg(dev->dev, "cdiv %d ckdiv %d hold %d (%d ns)\n",
                cdiv, ckdiv, hold, twd_hold_time_ns);
}

static void at91_twi_dma_cleanup(struct at91_twi_dev *dev)
{
        struct at91_twi_dma *dma = &dev->dma;

        at91_twi_irq_save(dev);

        if (dma->xfer_in_progress) {
                if (dma->direction == DMA_FROM_DEVICE)
                        dmaengine_terminate_all(dma->chan_rx);
                else
                        dmaengine_terminate_all(dma->chan_tx);
                dma->xfer_in_progress = false;
        }
        if (dma->buf_mapped) {
                dma_unmap_single(dev->dev, sg_dma_address(&dma->sg[0]),
                                 dev->buf_len, dma->direction);
                dma->buf_mapped = false;
        }

        at91_twi_irq_restore(dev);
}

static void at91_twi_write_next_byte(struct at91_twi_dev *dev)
{
        if (!dev->buf_len)
                return;

        /* 8bit write works with and without FIFO */
        writeb_relaxed(*dev->buf, dev->base + AT91_TWI_THR);

        /* send stop when last byte has been written */
        if (--dev->buf_len == 0)
                if (!dev->use_alt_cmd)
                        at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);

        dev_dbg(dev->dev, "wrote 0x%x, to go %zu\n", *dev->buf, dev->buf_len);

        ++dev->buf;
}

static void at91_twi_write_data_dma_callback(void *data)
{
        struct at91_twi_dev *dev = (struct at91_twi_dev *)data;

        dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg[0]),
                         dev->buf_len, DMA_TO_DEVICE);

        /*
         * When this callback is called, THR/TX FIFO is likely not to be empty
         * yet. So we have to wait for TXCOMP or NACK bits to be set into the
         * Status Register to be sure that the STOP bit has been sent and the
         * transfer is completed. The NACK interrupt has already been enabled,
         * we just have to enable TXCOMP one.
         */
        at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP);
        if (!dev->use_alt_cmd)
                at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
}

static void at91_twi_write_data_dma(struct at91_twi_dev *dev)
{
        dma_addr_t dma_addr;
        struct dma_async_tx_descriptor *txdesc;
        struct at91_twi_dma *dma = &dev->dma;
        struct dma_chan *chan_tx = dma->chan_tx;
        unsigned int sg_len = 1;

        if (!dev->buf_len)
                return;

        dma->direction = DMA_TO_DEVICE;

        at91_twi_irq_save(dev);
        dma_addr = dma_map_single(dev->dev, dev->buf, dev->buf_len,
                                  DMA_TO_DEVICE);
        if (dma_mapping_error(dev->dev, dma_addr)) {
                dev_err(dev->dev, "dma map failed\n");
                return;
        }
        dma->buf_mapped = true;
        at91_twi_irq_restore(dev);

        if (dev->fifo_size) {
                size_t part1_len, part2_len;
                struct scatterlist *sg;
                unsigned fifo_mr;

                sg_len = 0;

                part1_len = dev->buf_len & ~0x3;
                if (part1_len) {
                        sg = &dma->sg[sg_len++];
                        sg_dma_len(sg) = part1_len;
                        sg_dma_address(sg) = dma_addr;
                }

                part2_len = dev->buf_len & 0x3;
                if (part2_len) {
                        sg = &dma->sg[sg_len++];
                        sg_dma_len(sg) = part2_len;
                        sg_dma_address(sg) = dma_addr + part1_len;
                }

                /*
                 * DMA controller is triggered when at least 4 data can be
                 * written into the TX FIFO
                 */
                fifo_mr = at91_twi_read(dev, AT91_TWI_FMR);
                fifo_mr &= ~AT91_TWI_FMR_TXRDYM_MASK;
                fifo_mr |= AT91_TWI_FMR_TXRDYM(AT91_TWI_FOUR_DATA);
                at91_twi_write(dev, AT91_TWI_FMR, fifo_mr);
        } else {
                sg_dma_len(&dma->sg[0]) = dev->buf_len;
                sg_dma_address(&dma->sg[0]) = dma_addr;
        }

        txdesc = dmaengine_prep_slave_sg(chan_tx, dma->sg, sg_len,
                                         DMA_MEM_TO_DEV,
                                         DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
        if (!txdesc) {
                dev_err(dev->dev, "dma prep slave sg failed\n");
                goto error;
        }

        txdesc->callback = at91_twi_write_data_dma_callback;
        txdesc->callback_param = dev;

        dma->xfer_in_progress = true;
        dmaengine_submit(txdesc);
        dma_async_issue_pending(chan_tx);

        return;

error:
        at91_twi_dma_cleanup(dev);
}

static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
{
        /*
         * If we are in this case, it means there is garbage data in RHR, so
         * delete them.
         */
        if (!dev->buf_len) {
                at91_twi_read(dev, AT91_TWI_RHR);
                return;
        }

        /* 8bit read works with and without FIFO */
        *dev->buf = readb_relaxed(dev->base + AT91_TWI_RHR);
        --dev->buf_len;

        /* return if aborting, we only needed to read RHR to clear RXRDY*/
        if (dev->recv_len_abort)
                return;

        /* handle I2C_SMBUS_BLOCK_DATA */
        if (unlikely(dev->msg->flags & I2C_M_RECV_LEN)) {
                /* ensure length byte is a valid value */
                if (*dev->buf <= I2C_SMBUS_BLOCK_MAX && *dev->buf > 0) {
                        dev->msg->flags &= ~I2C_M_RECV_LEN;
                        dev->buf_len += *dev->buf;
                        dev->msg->len = dev->buf_len + 1;
                        dev_dbg(dev->dev, "received block length %zu\n",
                                         dev->buf_len);
                } else {
                        /* abort and send the stop by reading one more byte */
                        dev->recv_len_abort = true;
                        dev->buf_len = 1;
                }
        }

        /* send stop if second but last byte has been read */
        if (!dev->use_alt_cmd && dev->buf_len == 1)
                at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);

        dev_dbg(dev->dev, "read 0x%x, to go %zu\n", *dev->buf, dev->buf_len);

        ++dev->buf;
}

static void at91_twi_read_data_dma_callback(void *data)
{
        struct at91_twi_dev *dev = (struct at91_twi_dev *)data;
        unsigned ier = AT91_TWI_TXCOMP;

        dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg[0]),
                         dev->buf_len, DMA_FROM_DEVICE);

        if (!dev->use_alt_cmd) {
                /* The last two bytes have to be read without using dma */
                dev->buf += dev->buf_len - 2;
                dev->buf_len = 2;
                ier |= AT91_TWI_RXRDY;
        }
        at91_twi_write(dev, AT91_TWI_IER, ier);
}

static void at91_twi_read_data_dma(struct at91_twi_dev *dev)
{
        dma_addr_t dma_addr;
        struct dma_async_tx_descriptor *rxdesc;
        struct at91_twi_dma *dma = &dev->dma;
        struct dma_chan *chan_rx = dma->chan_rx;
        size_t buf_len;

        buf_len = (dev->use_alt_cmd) ? dev->buf_len : dev->buf_len - 2;
        dma->direction = DMA_FROM_DEVICE;

        /* Keep in mind that we won't use dma to read the last two bytes */
        at91_twi_irq_save(dev);
        dma_addr = dma_map_single(dev->dev, dev->buf, buf_len, DMA_FROM_DEVICE);
        if (dma_mapping_error(dev->dev, dma_addr)) {
                dev_err(dev->dev, "dma map failed\n");
                return;
        }
        dma->buf_mapped = true;
        at91_twi_irq_restore(dev);

        if (dev->fifo_size && IS_ALIGNED(buf_len, 4)) {
                unsigned fifo_mr;

                /*
                 * DMA controller is triggered when at least 4 data can be
                 * read from the RX FIFO
                 */
                fifo_mr = at91_twi_read(dev, AT91_TWI_FMR);
                fifo_mr &= ~AT91_TWI_FMR_RXRDYM_MASK;
                fifo_mr |= AT91_TWI_FMR_RXRDYM(AT91_TWI_FOUR_DATA);
                at91_twi_write(dev, AT91_TWI_FMR, fifo_mr);
        }

        sg_dma_len(&dma->sg[0]) = buf_len;
        sg_dma_address(&dma->sg[0]) = dma_addr;

        rxdesc = dmaengine_prep_slave_sg(chan_rx, dma->sg, 1, DMA_DEV_TO_MEM,
                                         DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
        if (!rxdesc) {
                dev_err(dev->dev, "dma prep slave sg failed\n");
                goto error;
        }

        rxdesc->callback = at91_twi_read_data_dma_callback;
        rxdesc->callback_param = dev;

        dma->xfer_in_progress = true;
        dmaengine_submit(rxdesc);
        dma_async_issue_pending(dma->chan_rx);

        return;

error:
        at91_twi_dma_cleanup(dev);
}

static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
{
        struct at91_twi_dev *dev = dev_id;
        const unsigned status = at91_twi_read(dev, AT91_TWI_SR);
        const unsigned irqstatus = status & at91_twi_read(dev, AT91_TWI_IMR);

        if (!irqstatus)
                return IRQ_NONE;
        /*
         * In reception, the behavior of the twi device (before sama5d2) is
         * weird. There is some magic about RXRDY flag! When a data has been
         * almost received, the reception of a new one is anticipated if there
         * is no stop command to send. That is the reason why ask for sending
         * the stop command not on the last data but on the second last one.
         *
         * Unfortunately, we could still have the RXRDY flag set even if the
         * transfer is done and we have read the last data. It might happen
         * when the i2c slave device sends too quickly data after receiving the
         * ack from the master. The data has been almost received before having
         * the order to send stop. In this case, sending the stop command could
         * cause a RXRDY interrupt with a TXCOMP one. It is better to manage
         * the RXRDY interrupt first in order to not keep garbage data in the
         * Receive Holding Register for the next transfer.
         */
        if (irqstatus & AT91_TWI_RXRDY)
                at91_twi_read_next_byte(dev);

        /*
         * When a NACK condition is detected, the I2C controller sets the NACK,
         * TXCOMP and TXRDY bits all together in the Status Register (SR).
         *
         * 1 - Handling NACK errors with CPU write transfer.
         *
         * In such case, we should not write the next byte into the Transmit
         * Holding Register (THR) otherwise the I2C controller would start a new
         * transfer and the I2C slave is likely to reply by another NACK.
         *
         * 2 - Handling NACK errors with DMA write transfer.
         *
         * By setting the TXRDY bit in the SR, the I2C controller also triggers
         * the DMA controller to write the next data into the THR. Then the
         * result depends on the hardware version of the I2C controller.
         *
         * 2a - Without support of the Alternative Command mode.
         *
         * This is the worst case: the DMA controller is triggered to write the
         * next data into the THR, hence starting a new transfer: the I2C slave
         * is likely to reply by another NACK.
         * Concurrently, this interrupt handler is likely to be called to manage
         * the first NACK before the I2C controller detects the second NACK and
         * sets once again the NACK bit into the SR.
         * When handling the first NACK, this interrupt handler disables the I2C
         * controller interruptions, especially the NACK interrupt.
         * Hence, the NACK bit is pending into the SR. This is why we should
         * read the SR to clear all pending interrupts at the beginning of
         * at91_do_twi_transfer() before actually starting a new transfer.
         *
         * 2b - With support of the Alternative Command mode.
         *
         * When a NACK condition is detected, the I2C controller also locks the
         * THR (and sets the LOCK bit in the SR): even though the DMA controller
         * is triggered by the TXRDY bit to write the next data into the THR,
         * this data actually won't go on the I2C bus hence a second NACK is not
         * generated.
         */
        if (irqstatus & (AT91_TWI_TXCOMP | AT91_TWI_NACK)) {
                at91_disable_twi_interrupts(dev);
                complete(&dev->cmd_complete);
        } else if (irqstatus & AT91_TWI_TXRDY) {
                at91_twi_write_next_byte(dev);
        }

        /* catch error flags */
        dev->transfer_status |= status;

        return IRQ_HANDLED;
}

static int at91_do_twi_transfer(struct at91_twi_dev *dev)
{
        int ret;
        unsigned long time_left;
        bool has_unre_flag = dev->pdata->has_unre_flag;
        bool has_alt_cmd = dev->pdata->has_alt_cmd;

        /*
         * WARNING: the TXCOMP bit in the Status Register is NOT a clear on
         * read flag but shows the state of the transmission at the time the
         * Status Register is read. According to the programmer datasheet,
         * TXCOMP is set when both holding register and internal shifter are
         * empty and STOP condition has been sent.
         * Consequently, we should enable NACK interrupt rather than TXCOMP to
         * detect transmission failure.
         * Indeed let's take the case of an i2c write command using DMA.
         * Whenever the slave doesn't acknowledge a byte, the LOCK, NACK and
         * TXCOMP bits are set together into the Status Register.
         * LOCK is a clear on write bit, which is set to prevent the DMA
         * controller from sending new data on the i2c bus after a NACK
         * condition has happened. Once locked, this i2c peripheral stops
         * triggering the DMA controller for new data but it is more than
         * likely that a new DMA transaction is already in progress, writing
         * into the Transmit Holding Register. Since the peripheral is locked,
         * these new data won't be sent to the i2c bus but they will remain
         * into the Transmit Holding Register, so TXCOMP bit is cleared.
         * Then when the interrupt handler is called, the Status Register is
         * read: the TXCOMP bit is clear but NACK bit is still set. The driver
         * manage the error properly, without waiting for timeout.
         * This case can be reproduced easyly when writing into an at24 eeprom.
         *
         * Besides, the TXCOMP bit is already set before the i2c transaction
         * has been started. For read transactions, this bit is cleared when
         * writing the START bit into the Control Register. So the
         * corresponding interrupt can safely be enabled just after.
         * However for write transactions managed by the CPU, we first write
         * into THR, so TXCOMP is cleared. Then we can safely enable TXCOMP
         * interrupt. If TXCOMP interrupt were enabled before writing into THR,
         * the interrupt handler would be called immediately and the i2c command
         * would be reported as completed.
         * Also when a write transaction is managed by the DMA controller,
         * enabling the TXCOMP interrupt in this function may lead to a race
         * condition since we don't know whether the TXCOMP interrupt is enabled
         * before or after the DMA has started to write into THR. So the TXCOMP
         * interrupt is enabled later by at91_twi_write_data_dma_callback().
         * Immediately after in that DMA callback, if the alternative command
         * mode is not used, we still need to send the STOP condition manually
         * writing the corresponding bit into the Control Register.
         */

        dev_dbg(dev->dev, "transfer: %s %zu bytes.\n",
                (dev->msg->flags & I2C_M_RD) ? "read" : "write", dev->buf_len);

        reinit_completion(&dev->cmd_complete);
        dev->transfer_status = 0;

        /* Clear pending interrupts, such as NACK. */
        at91_twi_read(dev, AT91_TWI_SR);

        if (dev->fifo_size) {
                unsigned fifo_mr = at91_twi_read(dev, AT91_TWI_FMR);

                /* Reset FIFO mode register */
                fifo_mr &= ~(AT91_TWI_FMR_TXRDYM_MASK |
                             AT91_TWI_FMR_RXRDYM_MASK);
                fifo_mr |= AT91_TWI_FMR_TXRDYM(AT91_TWI_ONE_DATA);
                fifo_mr |= AT91_TWI_FMR_RXRDYM(AT91_TWI_ONE_DATA);
                at91_twi_write(dev, AT91_TWI_FMR, fifo_mr);

                /* Flush FIFOs */
                at91_twi_write(dev, AT91_TWI_CR,
                               AT91_TWI_THRCLR | AT91_TWI_RHRCLR);
        }

        if (!dev->buf_len) {
                at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_QUICK);
                at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP);
        } else if (dev->msg->flags & I2C_M_RD) {
                unsigned start_flags = AT91_TWI_START;

                /* if only one byte is to be read, immediately stop transfer */
                if (!dev->use_alt_cmd && dev->buf_len <= 1 &&
                    !(dev->msg->flags & I2C_M_RECV_LEN))
                        start_flags |= AT91_TWI_STOP;
                at91_twi_write(dev, AT91_TWI_CR, start_flags);
                /*
                 * When using dma without alternative command mode, the last
                 * byte has to be read manually in order to not send the stop
                 * command too late and then to receive extra data.
                 * In practice, there are some issues if you use the dma to
                 * read n-1 bytes because of latency.
                 * Reading n-2 bytes with dma and the two last ones manually
                 * seems to be the best solution.
                 */
                if (dev->use_dma && (dev->buf_len > AT91_I2C_DMA_THRESHOLD)) {
                        at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_NACK);
                        at91_twi_read_data_dma(dev);
                } else {
                        at91_twi_write(dev, AT91_TWI_IER,
                                       AT91_TWI_TXCOMP |
                                       AT91_TWI_NACK |
                                       AT91_TWI_RXRDY);
                }
        } else {
                if (dev->use_dma && (dev->buf_len > AT91_I2C_DMA_THRESHOLD)) {
                        at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_NACK);
                        at91_twi_write_data_dma(dev);
                } else {
                        at91_twi_write_next_byte(dev);
                        at91_twi_write(dev, AT91_TWI_IER,
                                       AT91_TWI_TXCOMP |
                                       AT91_TWI_NACK |
                                       AT91_TWI_TXRDY);
                }
        }

        time_left = wait_for_completion_timeout(&dev->cmd_complete,
                                              dev->adapter.timeout);
        if (time_left == 0) {
                dev->transfer_status |= at91_twi_read(dev, AT91_TWI_SR);
                dev_err(dev->dev, "controller timed out\n");
                at91_init_twi_bus(dev);
                ret = -ETIMEDOUT;
                goto error;
        }
        if (dev->transfer_status & AT91_TWI_NACK) {
                dev_dbg(dev->dev, "received nack\n");
                ret = -EREMOTEIO;
                goto error;
        }
        if (dev->transfer_status & AT91_TWI_OVRE) {
                dev_err(dev->dev, "overrun while reading\n");
                ret = -EIO;
                goto error;
        }
        if (has_unre_flag && dev->transfer_status & AT91_TWI_UNRE) {
                dev_err(dev->dev, "underrun while writing\n");
                ret = -EIO;
                goto error;
        }
        if ((has_alt_cmd || dev->fifo_size) &&
            (dev->transfer_status & AT91_TWI_LOCK)) {
                dev_err(dev->dev, "tx locked\n");
                ret = -EIO;
                goto error;
        }
        if (dev->recv_len_abort) {
                dev_err(dev->dev, "invalid smbus block length recvd\n");
                ret = -EPROTO;
                goto error;
        }

        dev_dbg(dev->dev, "transfer complete\n");

        return 0;

error:
        /* first stop DMA transfer if still in progress */
        at91_twi_dma_cleanup(dev);
        /* then flush THR/FIFO and unlock TX if locked */
        if ((has_alt_cmd || dev->fifo_size) &&
            (dev->transfer_status & AT91_TWI_LOCK)) {
                dev_dbg(dev->dev, "unlock tx\n");
                at91_twi_write(dev, AT91_TWI_CR,
                               AT91_TWI_THRCLR | AT91_TWI_LOCKCLR);
        }
        return ret;
}

static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
{
        struct at91_twi_dev *dev = i2c_get_adapdata(adap);
        int ret;
        unsigned int_addr_flag = 0;
        struct i2c_msg *m_start = msg;
        bool is_read;

        dev_dbg(&adap->dev, "at91_xfer: processing %d messages:\n", num);

        ret = pm_runtime_get_sync(dev->dev);
        if (ret < 0)
                goto out;

        if (num == 2) {
                int internal_address = 0;
                int i;

                /* 1st msg is put into the internal address, start with 2nd */
                m_start = &msg[1];
                for (i = 0; i < msg->len; ++i) {
                        const unsigned addr = msg->buf[msg->len - 1 - i];

                        internal_address |= addr << (8 * i);
                        int_addr_flag += AT91_TWI_IADRSZ_1;
                }
                at91_twi_write(dev, AT91_TWI_IADR, internal_address);
        }

        dev->use_alt_cmd = false;
        is_read = (m_start->flags & I2C_M_RD);
        if (dev->pdata->has_alt_cmd) {
                if (m_start->len > 0 &&
                    m_start->len < AT91_I2C_MAX_ALT_CMD_DATA_SIZE) {
                        at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_ACMEN);
                        at91_twi_write(dev, AT91_TWI_ACR,
                                       AT91_TWI_ACR_DATAL(m_start->len) |
                                       ((is_read) ? AT91_TWI_ACR_DIR : 0));
                        dev->use_alt_cmd = true;
                } else {
                        at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_ACMDIS);
                }
        }

        at91_twi_write(dev, AT91_TWI_MMR,
                       (m_start->addr << 16) |
                       int_addr_flag |
                       ((!dev->use_alt_cmd && is_read) ? AT91_TWI_MREAD : 0));

        dev->buf_len = m_start->len;
        dev->buf = m_start->buf;
        dev->msg = m_start;
        dev->recv_len_abort = false;

        ret = at91_do_twi_transfer(dev);

        ret = (ret < 0) ? ret : num;
out:
        pm_runtime_mark_last_busy(dev->dev);
        pm_runtime_put_autosuspend(dev->dev);

        return ret;
}

/*
 * The hardware can handle at most two messages concatenated by a
 * repeated start via it's internal address feature.
 */
static const struct i2c_adapter_quirks at91_twi_quirks = {
        .flags = I2C_AQ_COMB | I2C_AQ_COMB_WRITE_FIRST | I2C_AQ_COMB_SAME_ADDR,
        .max_comb_1st_msg_len = 3,
};

static u32 at91_twi_func(struct i2c_adapter *adapter)
{
        return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL
                | I2C_FUNC_SMBUS_READ_BLOCK_DATA;
}

static const struct i2c_algorithm at91_twi_algorithm = {
        .master_xfer    = at91_twi_xfer,
        .functionality  = at91_twi_func,
};

static struct at91_twi_pdata at91rm9200_config = {
        .clk_max_div = 5,
        .clk_offset = 3,
        .has_unre_flag = true,
        .has_alt_cmd = false,
        .has_hold_field = false,
};

static struct at91_twi_pdata at91sam9261_config = {
        .clk_max_div = 5,
        .clk_offset = 4,
        .has_unre_flag = false,
        .has_alt_cmd = false,
        .has_hold_field = false,
};

static struct at91_twi_pdata at91sam9260_config = {
        .clk_max_div = 7,
        .clk_offset = 4,
        .has_unre_flag = false,
        .has_alt_cmd = false,
        .has_hold_field = false,
};

static struct at91_twi_pdata at91sam9g20_config = {
        .clk_max_div = 7,
        .clk_offset = 4,
        .has_unre_flag = false,
        .has_alt_cmd = false,
        .has_hold_field = false,
};

static struct at91_twi_pdata at91sam9g10_config = {
        .clk_max_div = 7,
        .clk_offset = 4,
        .has_unre_flag = false,
        .has_alt_cmd = false,
        .has_hold_field = false,
};

static const struct platform_device_id at91_twi_devtypes[] = {
        {
                .name = "i2c-at91rm9200",
                .driver_data = (unsigned long) &at91rm9200_config,
        }, {
                .name = "i2c-at91sam9261",
                .driver_data = (unsigned long) &at91sam9261_config,
        }, {
                .name = "i2c-at91sam9260",
                .driver_data = (unsigned long) &at91sam9260_config,
        }, {
                .name = "i2c-at91sam9g20",
                .driver_data = (unsigned long) &at91sam9g20_config,
        }, {
                .name = "i2c-at91sam9g10",
                .driver_data = (unsigned long) &at91sam9g10_config,
        }, {
                /* sentinel */
        }
};

#if defined(CONFIG_OF)
static struct at91_twi_pdata at91sam9x5_config = {
        .clk_max_div = 7,
        .clk_offset = 4,
        .has_unre_flag = false,
        .has_alt_cmd = false,
        .has_hold_field = false,
};

static struct at91_twi_pdata sama5d4_config = {
        .clk_max_div = 7,
        .clk_offset = 4,
        .has_unre_flag = false,
        .has_alt_cmd = false,
        .has_hold_field = true,
};

static struct at91_twi_pdata sama5d2_config = {
        .clk_max_div = 7,
        .clk_offset = 4,
        .has_unre_flag = true,
        .has_alt_cmd = true,
        .has_hold_field = true,
};

static const struct of_device_id atmel_twi_dt_ids[] = {
        {
                .compatible = "atmel,at91rm9200-i2c",
                .data = &at91rm9200_config,
        } , {
                .compatible = "atmel,at91sam9260-i2c",
                .data = &at91sam9260_config,
        } , {
                .compatible = "atmel,at91sam9261-i2c",
                .data = &at91sam9261_config,
        } , {
                .compatible = "atmel,at91sam9g20-i2c",
                .data = &at91sam9g20_config,
        } , {
                .compatible = "atmel,at91sam9g10-i2c",
                .data = &at91sam9g10_config,
        }, {
                .compatible = "atmel,at91sam9x5-i2c",
                .data = &at91sam9x5_config,
        }, {
                .compatible = "atmel,sama5d4-i2c",
                .data = &sama5d4_config,
        }, {
                .compatible = "atmel,sama5d2-i2c",
                .data = &sama5d2_config,
        }, {
                /* sentinel */
        }
};
MODULE_DEVICE_TABLE(of, atmel_twi_dt_ids);
#endif

static int at91_twi_configure_dma(struct at91_twi_dev *dev, u32 phy_addr)
{
        int ret = 0;
        struct dma_slave_config slave_config;
        struct at91_twi_dma *dma = &dev->dma;
        enum dma_slave_buswidth addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;

        /*
         * The actual width of the access will be chosen in
         * dmaengine_prep_slave_sg():
         * for each buffer in the scatter-gather list, if its size is aligned
         * to addr_width then addr_width accesses will be performed to transfer
         * the buffer. On the other hand, if the buffer size is not aligned to
         * addr_width then the buffer is transferred using single byte accesses.
         * Please refer to the Atmel eXtended DMA controller driver.
         * When FIFOs are used, the TXRDYM threshold can always be set to
         * trigger the XDMAC when at least 4 data can be written into the TX
         * FIFO, even if single byte accesses are performed.
         * However the RXRDYM threshold must be set to fit the access width,
         * deduced from buffer length, so the XDMAC is triggered properly to
         * read data from the RX FIFO.
         */
        if (dev->fifo_size)
                addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;

        memset(&slave_config, 0, sizeof(slave_config));
        slave_config.src_addr = (dma_addr_t)phy_addr + AT91_TWI_RHR;
        slave_config.src_addr_width = addr_width;
        slave_config.src_maxburst = 1;
        slave_config.dst_addr = (dma_addr_t)phy_addr + AT91_TWI_THR;
        slave_config.dst_addr_width = addr_width;
        slave_config.dst_maxburst = 1;
        slave_config.device_fc = false;

        dma->chan_tx = dma_request_slave_channel_reason(dev->dev, "tx");
        if (IS_ERR(dma->chan_tx)) {
                ret = PTR_ERR(dma->chan_tx);
                dma->chan_tx = NULL;
                goto error;
        }

        dma->chan_rx = dma_request_slave_channel_reason(dev->dev, "rx");
        if (IS_ERR(dma->chan_rx)) {
                ret = PTR_ERR(dma->chan_rx);
                dma->chan_rx = NULL;
                goto error;
        }

        slave_config.direction = DMA_MEM_TO_DEV;
        if (dmaengine_slave_config(dma->chan_tx, &slave_config)) {
                dev_err(dev->dev, "failed to configure tx channel\n");
                ret = -EINVAL;
                goto error;
        }

        slave_config.direction = DMA_DEV_TO_MEM;
        if (dmaengine_slave_config(dma->chan_rx, &slave_config)) {
                dev_err(dev->dev, "failed to configure rx channel\n");
                ret = -EINVAL;
                goto error;
        }

        sg_init_table(dma->sg, 2);
        dma->buf_mapped = false;
        dma->xfer_in_progress = false;
        dev->use_dma = true;

        dev_info(dev->dev, "using %s (tx) and %s (rx) for DMA transfers\n",
                 dma_chan_name(dma->chan_tx), dma_chan_name(dma->chan_rx));

        return ret;

error:
        if (ret != -EPROBE_DEFER)
                dev_info(dev->dev, "can't get DMA channel, continue without DMA support\n");
        if (dma->chan_rx)
                dma_release_channel(dma->chan_rx);
        if (dma->chan_tx)
                dma_release_channel(dma->chan_tx);
        return ret;
}

static struct at91_twi_pdata *at91_twi_get_driver_data(
                                        struct platform_device *pdev)
{
        if (pdev->dev.of_node) {
                const struct of_device_id *match;
                match = of_match_node(atmel_twi_dt_ids, pdev->dev.of_node);
                if (!match)
                        return NULL;
                return (struct at91_twi_pdata *)match->data;
        }
        return (struct at91_twi_pdata *) platform_get_device_id(pdev)->driver_data;
}

static int at91_twi_probe(struct platform_device *pdev)
{
        struct at91_twi_dev *dev;
        struct resource *mem;
        int rc;
        u32 phy_addr;
        u32 bus_clk_rate;

        dev = devm_kzalloc(&pdev->dev, sizeof(*dev), GFP_KERNEL);
        if (!dev)
                return -ENOMEM;
        init_completion(&dev->cmd_complete);
        dev->dev = &pdev->dev;

        mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (!mem)
                return -ENODEV;
        phy_addr = mem->start;

        dev->pdata = at91_twi_get_driver_data(pdev);
        if (!dev->pdata)
                return -ENODEV;

        dev->base = devm_ioremap_resource(&pdev->dev, mem);
        if (IS_ERR(dev->base))
                return PTR_ERR(dev->base);

        dev->irq = platform_get_irq(pdev, 0);
        if (dev->irq < 0)
                return dev->irq;

        rc = devm_request_irq(&pdev->dev, dev->irq, atmel_twi_interrupt, 0,
                         dev_name(dev->dev), dev);
        if (rc) {
                dev_err(dev->dev, "Cannot get irq %d: %d\n", dev->irq, rc);
                return rc;
        }

        platform_set_drvdata(pdev, dev);

        dev->clk = devm_clk_get(dev->dev, NULL);
        if (IS_ERR(dev->clk)) {
                dev_err(dev->dev, "no clock defined\n");
                return -ENODEV;
        }
        rc = clk_prepare_enable(dev->clk);
        if (rc)
                return rc;

        if (dev->dev->of_node) {
                rc = at91_twi_configure_dma(dev, phy_addr);
                if (rc == -EPROBE_DEFER) {
                        clk_disable_unprepare(dev->clk);
                        return rc;
                }
        }

        if (!of_property_read_u32(pdev->dev.of_node, "atmel,fifo-size",
                                  &dev->fifo_size)) {
                dev_info(dev->dev, "Using FIFO (%u data)\n", dev->fifo_size);
        }

        rc = of_property_read_u32(dev->dev->of_node, "clock-frequency",
                        &bus_clk_rate);
        if (rc)
                bus_clk_rate = DEFAULT_TWI_CLK_HZ;

        at91_calc_twi_clock(dev, bus_clk_rate);
        at91_init_twi_bus(dev);

        snprintf(dev->adapter.name, sizeof(dev->adapter.name), "AT91");
        i2c_set_adapdata(&dev->adapter, dev);
        dev->adapter.owner = THIS_MODULE;
        dev->adapter.class = I2C_CLASS_DEPRECATED;
        dev->adapter.algo = &at91_twi_algorithm;
        dev->adapter.quirks = &at91_twi_quirks;
        dev->adapter.dev.parent = dev->dev;
        dev->adapter.nr = pdev->id;
        dev->adapter.timeout = AT91_I2C_TIMEOUT;
        dev->adapter.dev.of_node = pdev->dev.of_node;

        pm_runtime_set_autosuspend_delay(dev->dev, AUTOSUSPEND_TIMEOUT);
        pm_runtime_use_autosuspend(dev->dev);
        pm_runtime_set_active(dev->dev);
        pm_runtime_enable(dev->dev);

        rc = i2c_add_numbered_adapter(&dev->adapter);
        if (rc) {
                clk_disable_unprepare(dev->clk);

                pm_runtime_disable(dev->dev);
                pm_runtime_set_suspended(dev->dev);

                return rc;
        }

        dev_info(dev->dev, "AT91 i2c bus driver (hw version: %#x).\n",
                 at91_twi_read(dev, AT91_TWI_VER));
        return 0;
}

static int at91_twi_remove(struct platform_device *pdev)
{
        struct at91_twi_dev *dev = platform_get_drvdata(pdev);

        i2c_del_adapter(&dev->adapter);
        clk_disable_unprepare(dev->clk);

        pm_runtime_disable(dev->dev);
        pm_runtime_set_suspended(dev->dev);

        return 0;
}

#ifdef CONFIG_PM

static int at91_twi_runtime_suspend(struct device *dev)
{
        struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);

        clk_disable_unprepare(twi_dev->clk);

        pinctrl_pm_select_sleep_state(dev);

        return 0;
}

static int at91_twi_runtime_resume(struct device *dev)
{
        struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);

        pinctrl_pm_select_default_state(dev);

        return clk_prepare_enable(twi_dev->clk);
}

static int at91_twi_suspend_noirq(struct device *dev)
{
        if (!pm_runtime_status_suspended(dev))
                at91_twi_runtime_suspend(dev);

        return 0;
}

static int at91_twi_resume_noirq(struct device *dev)
{
        struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
        int ret;

        if (!pm_runtime_status_suspended(dev)) {
                ret = at91_twi_runtime_resume(dev);
                if (ret)
                        return ret;
        }

        pm_runtime_mark_last_busy(dev);
        pm_request_autosuspend(dev);

        at91_init_twi_bus(twi_dev);

        return 0;
}

static const struct dev_pm_ops at91_twi_pm = {
        .suspend_noirq  = at91_twi_suspend_noirq,
        .resume_noirq   = at91_twi_resume_noirq,
        .runtime_suspend        = at91_twi_runtime_suspend,
        .runtime_resume         = at91_twi_runtime_resume,
};

#define at91_twi_pm_ops (&at91_twi_pm)
#else
#define at91_twi_pm_ops NULL
#endif

static struct platform_driver at91_twi_driver = {
        .probe          = at91_twi_probe,
        .remove         = at91_twi_remove,
        .id_table       = at91_twi_devtypes,
        .driver         = {
                .name   = "at91_i2c",
                .of_match_table = of_match_ptr(atmel_twi_dt_ids),
                .pm     = at91_twi_pm_ops,
        },
};

static int __init at91_twi_init(void)
{
        return platform_driver_register(&at91_twi_driver);
}

static void __exit at91_twi_exit(void)
{
        platform_driver_unregister(&at91_twi_driver);
}

subsys_initcall(at91_twi_init);
module_exit(at91_twi_exit);

MODULE_AUTHOR("Nikolaus Voss <n.voss@weinmann.de>");
MODULE_DESCRIPTION("I2C (TWI) driver for Atmel AT91");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:at91_i2c");