Merge tag 'io_uring-5.7-2020-05-22' of git://git.kernel.dk/linux-block

[thirdparty/linux.git] / drivers / i2c / busses / i2c-at91-master.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  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>
 */

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

#include "i2c-at91.h"

void at91_init_twi_bus_master(struct at91_twi_dev *dev)
{
        struct at91_twi_pdata *pdata = dev->pdata;
        u32 filtr = 0;

        /* 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);

        /* enable digital filter */
        if (pdata->has_dig_filtr && dev->enable_dig_filt)
                filtr |= AT91_TWI_FILTR_FILT;

        /* enable advanced digital filter */
        if (pdata->has_adv_dig_filtr && dev->enable_dig_filt)
                filtr |= AT91_TWI_FILTR_FILT |
                         (AT91_TWI_FILTR_THRES(dev->filter_width) &
                         AT91_TWI_FILTR_THRES_MASK);

        /* enable analog filter */
        if (pdata->has_ana_filtr && dev->enable_ana_filt)
                filtr |= AT91_TWI_FILTR_PADFEN;

        if (filtr)
                at91_twi_write(dev, AT91_TWI_FILTR, filtr);
}

/*
 * 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 ckdiv, cdiv, div, hold = 0, filter_width = 0;
        struct at91_twi_pdata *pdata = dev->pdata;
        int offset = pdata->clk_offset;
        int max_ckdiv = pdata->clk_max_div;
        struct i2c_timings timings, *t = &timings;

        i2c_parse_fw_timings(dev->dev, t, true);

        div = max(0, (int)DIV_ROUND_UP(clk_get_rate(dev->clk),
                                       2 * t->bus_freq_hz) - 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) {
                /*
                 * hold time = HOLD + 3 x T_peripheral_clock
                 * Use clk rate in kHz to prevent overflows when computing
                 * hold.
                 */
                hold = DIV_ROUND_UP(t->sda_hold_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;
                }
        }

        if (pdata->has_adv_dig_filtr) {
                /*
                 * filter width = 0 to AT91_TWI_FILTR_THRES_MAX
                 * peripheral clocks
                 */
                filter_width = DIV_ROUND_UP(t->digital_filter_width_ns
                                * (clk_get_rate(dev->clk) / 1000), 1000000);
                if (filter_width > AT91_TWI_FILTR_THRES_MAX) {
                        dev_warn(dev->dev,
                                "Filter threshold set to its maximum value (%d instead of %d)\n",
                                AT91_TWI_FILTR_THRES_MAX, filter_width);
                        filter_width = AT91_TWI_FILTR_THRES_MAX;
                }
        }

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

        dev->filter_width = filter_width;

        dev_dbg(dev->dev, "cdiv %d ckdiv %d hold %d (%d ns), filter_width %d (%d ns)\n",
                cdiv, ckdiv, hold, t->sda_hold_ns, filter_width,
                t->digital_filter_width_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);
                at91_twi_write(dev, AT91_TWI_IDR, AT91_TWI_TXRDY);
        }

        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) {
                /*
                 * Read all available bytes at once by polling RXRDY usable w/
                 * and w/o FIFO. With FIFO enabled we could also read RXFL and
                 * avoid polling RXRDY.
                 */
                do {
                        at91_twi_read_next_byte(dev);
                } while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
        }

        /*
         * 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;
        struct i2c_bus_recovery_info *rinfo = &dev->rinfo;

        /*
         * 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 |
                                       (dev->buf_len ? AT91_TWI_TXRDY : 0));
                }
        }

        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);
        }

        if (rinfo->get_sda && !(rinfo->get_sda(&dev->adapter))) {
                dev_dbg(dev->dev,
                        "SDA is down; clear bus using gpio\n");
                i2c_recover_bus(&dev->adapter);
        }

        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 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_chan(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_chan(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 void at91_prepare_twi_recovery(struct i2c_adapter *adap)
{
        struct at91_twi_dev *dev = i2c_get_adapdata(adap);

        pinctrl_select_state(dev->pinctrl, dev->pinctrl_pins_gpio);
}

static void at91_unprepare_twi_recovery(struct i2c_adapter *adap)
{
        struct at91_twi_dev *dev = i2c_get_adapdata(adap);

        pinctrl_select_state(dev->pinctrl, dev->pinctrl_pins_default);
}

static int at91_init_twi_recovery_info(struct platform_device *pdev,
                                       struct at91_twi_dev *dev)
{
        struct i2c_bus_recovery_info *rinfo = &dev->rinfo;

        dev->pinctrl = devm_pinctrl_get(&pdev->dev);
        if (!dev->pinctrl || IS_ERR(dev->pinctrl)) {
                dev_info(dev->dev, "can't get pinctrl, bus recovery not supported\n");
                return PTR_ERR(dev->pinctrl);
        }

        dev->pinctrl_pins_default = pinctrl_lookup_state(dev->pinctrl,
                                                         PINCTRL_STATE_DEFAULT);
        dev->pinctrl_pins_gpio = pinctrl_lookup_state(dev->pinctrl,
                                                      "gpio");
        if (IS_ERR(dev->pinctrl_pins_default) ||
            IS_ERR(dev->pinctrl_pins_gpio)) {
                dev_info(&pdev->dev, "pinctrl states incomplete for recovery\n");
                return -EINVAL;
        }

        /*
         * pins will be taken as GPIO, so we might as well inform pinctrl about
         * this and move the state to GPIO
         */
        pinctrl_select_state(dev->pinctrl, dev->pinctrl_pins_gpio);

        rinfo->sda_gpiod = devm_gpiod_get(&pdev->dev, "sda", GPIOD_IN);
        if (PTR_ERR(rinfo->sda_gpiod) == -EPROBE_DEFER)
                return -EPROBE_DEFER;

        rinfo->scl_gpiod = devm_gpiod_get(&pdev->dev, "scl",
                                          GPIOD_OUT_HIGH_OPEN_DRAIN);
        if (PTR_ERR(rinfo->scl_gpiod) == -EPROBE_DEFER)
                return -EPROBE_DEFER;

        if (IS_ERR(rinfo->sda_gpiod) ||
            IS_ERR(rinfo->scl_gpiod)) {
                dev_info(&pdev->dev, "recovery information incomplete\n");
                if (!IS_ERR(rinfo->sda_gpiod)) {
                        gpiod_put(rinfo->sda_gpiod);
                        rinfo->sda_gpiod = NULL;
                }
                if (!IS_ERR(rinfo->scl_gpiod)) {
                        gpiod_put(rinfo->scl_gpiod);
                        rinfo->scl_gpiod = NULL;
                }
                pinctrl_select_state(dev->pinctrl, dev->pinctrl_pins_default);
                return -EINVAL;
        }

        /* change the state of the pins back to their default state */
        pinctrl_select_state(dev->pinctrl, dev->pinctrl_pins_default);

        dev_info(&pdev->dev, "using scl, sda for recovery\n");

        rinfo->prepare_recovery = at91_prepare_twi_recovery;
        rinfo->unprepare_recovery = at91_unprepare_twi_recovery;
        rinfo->recover_bus = i2c_generic_scl_recovery;
        dev->adapter.bus_recovery_info = rinfo;

        return 0;
}

int at91_twi_probe_master(struct platform_device *pdev,
                          u32 phy_addr, struct at91_twi_dev *dev)
{
        int rc;

        init_completion(&dev->cmd_complete);

        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;
        }

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

        dev->enable_dig_filt = of_property_read_bool(pdev->dev.of_node,
                                                     "i2c-digital-filter");

        dev->enable_ana_filt = of_property_read_bool(pdev->dev.of_node,
                                                     "i2c-analog-filter");
        at91_calc_twi_clock(dev);

        rc = at91_init_twi_recovery_info(pdev, dev);
        if (rc == -EPROBE_DEFER)
                return rc;

        dev->adapter.algo = &at91_twi_algorithm;
        dev->adapter.quirks = &at91_twi_quirks;

        return 0;
}