drm/radeon: clarify special handling in i2c over aux

We need a special packet for the start and end of the
transaction.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>

diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
index 88d399c..23189b7 100644 (file)
--- a/drivers/gpu/drm/radeon/atombios_dp.c
+++ b/drivers/gpu/drm/radeon/atombios_dp.c
@@ -246,34 +246,30 @@ int radeon_dp_i2c_aux_ch(struct i2c_adapter *adapter, int mode,
        int ret;
        u8 ack;
 
-       /* Set up the command byte */
-       if (mode & MODE_I2C_READ)
-               msg[2] = DP_AUX_I2C_READ << 4;
-       else
-               msg[2] = DP_AUX_I2C_WRITE << 4;
-
-       if (!(mode & MODE_I2C_STOP))
-               msg[2] |= DP_AUX_I2C_MOT << 4;
-
+       /* Set up the address */
        msg[0] = address;
        msg[1] = address >> 8;
 
-       switch (mode) {
-       case MODE_I2C_WRITE:
+       /* Set up the command byte */
+       if (mode & MODE_I2C_READ) {
+               msg[2] = DP_AUX_I2C_READ << 4;
+               msg_bytes = 4;
+               msg[3] = msg_bytes << 4;
+       } else {
+               msg[2] = DP_AUX_I2C_WRITE << 4;
                msg_bytes = 5;
                msg[3] = msg_bytes << 4;
                msg[4] = write_byte;
-               break;
-       case MODE_I2C_READ:
-               msg_bytes = 4;
-               msg[3] = msg_bytes << 4;
-               break;
-       default:
-               msg_bytes = 4;
-               msg[3] = 3 << 4;
-               break;
        }
 
+       /* special handling for start/stop */
+       if (mode & (MODE_I2C_START | MODE_I2C_STOP))
+               msg[3] = 3 << 4;
+
+       /* Set MOT bit for all but stop */
+       if ((mode & MODE_I2C_STOP) == 0)
+               msg[2] |= DP_AUX_I2C_MOT << 4;
+
        for (retry = 0; retry < 7; retry++) {
                ret = radeon_process_aux_ch(auxch,
                                            msg, msg_bytes, reply, reply_bytes, 0, &ack);