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    Subject[PATCH 5.15 362/779] i2c: cadence: Support PEC for SMBus block read
    Date
    From: Lars-Peter Clausen <lars@metafoo.de>

    [ Upstream commit 9fdf6d97f03035ad5298e2d1635036c74c2090ed ]

    SMBus packet error checking (PEC) is implemented by appending one
    additional byte of checksum data at the end of the message. This provides
    additional protection and allows to detect data corruption on the I2C bus.

    SMBus block reads support variable length reads. The first byte in the read
    message is the number of available data bytes.

    The combination of PEC and block read is currently not supported by the
    Cadence I2C driver.
    * When PEC is enabled the maximum transfer length for block reads
    increases from 33 to 34 bytes.
    * The I2C core smbus emulation layer relies on the driver updating the
    `i2c_msg` `len` field with the number of received bytes. The updated
    length is used when checking the PEC.

    Add support to the Cadence I2C driver for handling SMBus block reads with
    PEC. To determine the maximum transfer length uses the initial `len` value
    of the `i2c_msg`. When PEC is enabled this will be 2, when it is disabled
    it will be 1.

    Once a read transfer is done also increment the `len` field by the amount
    of received data bytes.

    This change has been tested with a UCM90320 PMBus power monitor, which
    requires block reads to access certain data fields, but also has PEC
    enabled by default.

    Fixes: df8eb5691c48 ("i2c: Add driver for Cadence I2C controller")
    Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
    Tested-by: Shubhrajyoti Datta <Shubhrajyoti.datta@amd.com>
    Signed-off-by: Wolfram Sang <wsa@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/i2c/busses/i2c-cadence.c | 10 +++++++++-
    1 file changed, 9 insertions(+), 1 deletion(-)

    diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
    index 630cfa4ddd46..33f5588a50c0 100644
    --- a/drivers/i2c/busses/i2c-cadence.c
    +++ b/drivers/i2c/busses/i2c-cadence.c
    @@ -573,8 +573,13 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id)
    ctrl_reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
    ctrl_reg |= CDNS_I2C_CR_RW | CDNS_I2C_CR_CLR_FIFO;

    + /*
    + * Receive up to I2C_SMBUS_BLOCK_MAX data bytes, plus one message length
    + * byte, plus one checksum byte if PEC is enabled. p_msg->len will be 2 if
    + * PEC is enabled, otherwise 1.
    + */
    if (id->p_msg->flags & I2C_M_RECV_LEN)
    - id->recv_count = I2C_SMBUS_BLOCK_MAX + 1;
    + id->recv_count = I2C_SMBUS_BLOCK_MAX + id->p_msg->len;

    id->curr_recv_count = id->recv_count;

    @@ -789,6 +794,9 @@ static int cdns_i2c_process_msg(struct cdns_i2c *id, struct i2c_msg *msg,
    if (id->err_status & CDNS_I2C_IXR_ARB_LOST)
    return -EAGAIN;

    + if (msg->flags & I2C_M_RECV_LEN)
    + msg->len += min_t(unsigned int, msg->buf[0], I2C_SMBUS_BLOCK_MAX);
    +
    return 0;
    }

    --
    2.35.1


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