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    Subject[PATCH 3.16 167/294] i2c: ismt: Don't duplicate the receive length for block reads
    3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Stephen Douthit <stephend@adiengineering.com>

    commit b6c159a9cb69c2cf0bf59d4e12c3a2da77e4d994 upstream.

    According to Table 15-14 of the C2000 EDS (Intel doc #510524) the
    rx data pointed to by the descriptor dptr contains the byte count.

    desc->rxbytes reports all bytes read on the wire, including the
    "byte count" byte. So if a device sends 4 bytes in response to a
    block read, on the wire and in the DMA buffer we see:

    count data1 data2 data3 data4
    0x04 0xde 0xad 0xbe 0xef

    That's what we want to return in data->block to the next level.

    Instead we were actually prefixing that with desc->rxbytes:

    bad
    count count data1 data2 data3 data4
    0x05 0x04 0xde 0xad 0xbe 0xef

    This was discovered while developing a BMC solution relying on the
    ipmi_ssif.c driver which was trying to interpret the bogus length
    field as part of the IPMI response.

    Signed-off-by: Stephen Douthit <stephend@adiengineering.com>
    Tested-by: Dan Priamo <danp@adiengineering.com>
    Acked-by: Neil Horman <nhorman@tuxdriver.com>
    Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/i2c/busses/i2c-ismt.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/drivers/i2c/busses/i2c-ismt.c
    +++ b/drivers/i2c/busses/i2c-ismt.c
    @@ -344,8 +344,8 @@ static int ismt_process_desc(const struc
    break;
    case I2C_SMBUS_BLOCK_DATA:
    case I2C_SMBUS_I2C_BLOCK_DATA:
    - memcpy(&data->block[1], dma_buffer, desc->rxbytes);
    - data->block[0] = desc->rxbytes;
    + memcpy(data->block, dma_buffer, desc->rxbytes);
    + data->block[0] = desc->rxbytes - 1;
    break;
    }
    return 0;
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