• Eudean Sun's avatar
    HID: cp2112: Fix I2C_BLOCK_DATA transactions · 542134c0
    Eudean Sun authored
    The existing driver erroneously treats I2C_BLOCK_DATA and BLOCK_DATA
    commands the same.
    
    For I2C_BLOCK_DATA reads, the length of the read is provided in
    data->block[0], but the length itself should not be sent to the slave. In
    contrast, for BLOCK_DATA reads no length is specified since the length
    will be the first byte returned from the slave. When copying data back
    to the data buffer, for an I2C_BLOCK_DATA read we have to take care not to
    overwrite data->block[0] to avoid overwriting the length. A BLOCK_DATA
    read doesn't have this concern since the first byte returned by the device
    is the length and belongs in data->block[0].
    
    For I2C_BLOCK_DATA writes, the length is also provided in data->block[0],
    but the length itself is not sent to the slave (in contrast to BLOCK_DATA
    writes where the length prefixes the data sent to the slave).
    
    This was tested on physical hardware using i2cdump with the i and s flags
    to test the behavior of I2C_BLOCK_DATA reads and BLOCK_DATA reads,
    respectively. Writes were not tested but the I2C_BLOCK_DATA write change
    is pretty simple to verify by inspection.
    Signed-off-by: 's avatarEudean Sun <eudean@arista.com>
    Signed-off-by: 's avatarJiri Kosina <jkosina@suse.cz>
    542134c0
hid-cp2112.c 36.4 KB