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    Subject[PATCH v3 3/6] i2c: at91: Send bus clear command if SDA is down
    Date
    After a transfer timeout, some faulty I2C slave devices might hold down
    the SDA pin. We can generate a bus clear command, hoping that the slave
    might release the pins.
    If the CLEAR command is not supported, we will use gpio recovery, if
    available, to reset the bus.

    Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
    ---

    Changes in v3:
    - rebased on top of i2c/for-next;
    - remove unnecessary initializations with false;
    - replaced SCL with SDA in title and commit message;
    - updated commit message;

    Changes in v2:
    - use CLEAR command only if SDA is down; update patch subject to
    reflect this;
    - CLEAR command is no longer used for sama5d2, only sam9x60;

    drivers/i2c/busses/i2c-at91-core.c | 2 ++
    drivers/i2c/busses/i2c-at91-master.c | 32 +++++++++++++++++++++++-----
    drivers/i2c/busses/i2c-at91.h | 7 +++++-
    3 files changed, 35 insertions(+), 6 deletions(-)

    diff --git a/drivers/i2c/busses/i2c-at91-core.c b/drivers/i2c/busses/i2c-at91-core.c
    index 3da1a8acecb5..e14edd236108 100644
    --- a/drivers/i2c/busses/i2c-at91-core.c
    +++ b/drivers/i2c/busses/i2c-at91-core.c
    @@ -131,6 +131,7 @@ static struct at91_twi_pdata sama5d2_config = {
    .has_dig_filtr = true,
    .has_adv_dig_filtr = true,
    .has_ana_filtr = true,
    + .has_clear_cmd = false, /* due to errata, CLEAR cmd is not working */
    };

    static struct at91_twi_pdata sam9x60_config = {
    @@ -142,6 +143,7 @@ static struct at91_twi_pdata sam9x60_config = {
    .has_dig_filtr = true,
    .has_adv_dig_filtr = true,
    .has_ana_filtr = true,
    + .has_clear_cmd = true,
    };

    static const struct of_device_id atmel_twi_dt_ids[] = {
    diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
    index 0aba51a7df32..bcc05a8fe826 100644
    --- a/drivers/i2c/busses/i2c-at91-master.c
    +++ b/drivers/i2c/busses/i2c-at91-master.c
    @@ -480,7 +480,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
    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;
    + bool has_clear_cmd = dev->pdata->has_clear_cmd;

    /*
    * WARNING: the TXCOMP bit in the Status Register is NOT a clear on
    @@ -641,10 +641,32 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
    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);
    + /*
    + * some faulty I2C slave devices might hold SDA down;
    + * we can send a bus clear command, hoping that the pins will be
    + * released
    + */
    + if (has_clear_cmd) {
    + if (!(dev->transfer_status & AT91_TWI_SDA)) {
    + dev_dbg(dev->dev,
    + "SDA is down; sending bus clear command\n");
    + if (dev->use_alt_cmd) {
    + unsigned int acr;
    +
    + acr = at91_twi_read(dev, AT91_TWI_ACR);
    + acr &= ~AT91_TWI_ACR_DATAL_MASK;
    + at91_twi_write(dev, AT91_TWI_ACR, acr);
    + }
    + at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_CLEAR);
    + }
    + } else {
    + struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
    +
    + 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;
    diff --git a/drivers/i2c/busses/i2c-at91.h b/drivers/i2c/busses/i2c-at91.h
    index f57a6cab96b4..7e7b4955ca7f 100644
    --- a/drivers/i2c/busses/i2c-at91.h
    +++ b/drivers/i2c/busses/i2c-at91.h
    @@ -36,6 +36,7 @@
    #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_CLEAR BIT(15) /* Bus clear command */
    #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 */
    @@ -69,6 +70,8 @@
    #define AT91_TWI_NACK BIT(8) /* Not Acknowledged */
    #define AT91_TWI_EOSACC BIT(11) /* End Of Slave Access */
    #define AT91_TWI_LOCK BIT(23) /* TWI Lock due to Frame Errors */
    +#define AT91_TWI_SCL BIT(24) /* TWI SCL status */
    +#define AT91_TWI_SDA BIT(25) /* TWI SDA status */

    #define AT91_TWI_INT_MASK \
    (AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY | AT91_TWI_NACK \
    @@ -81,7 +84,8 @@
    #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_DATAL_MASK GENMASK(15, 0)
    +#define AT91_TWI_ACR_DATAL(len) ((len) & AT91_TWI_ACR_DATAL_MASK)
    #define AT91_TWI_ACR_DIR BIT(8)

    #define AT91_TWI_FILTR 0x0044
    @@ -118,6 +122,7 @@ struct at91_twi_pdata {
    bool has_dig_filtr;
    bool has_adv_dig_filtr;
    bool has_ana_filtr;
    + bool has_clear_cmd;
    struct at_dma_slave dma_slave;
    };

    --
    2.20.1
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