drm/amd/display: Correct the reply value when AUX write incomplete

[Why]
Now forcing aux->transfer to return 0 when incomplete AUX write is
inappropriate. It should return bytes have been transferred.

[How]
aux->transfer is asked not to change original msg except reply field of
drm_dp_aux_msg structure. Copy the msg->buffer when it's write request,
and overwrite the first byte when sink reply 1 byte indicating partially
written byte number. Then we can return the correct value without
changing the original msg.

Fixes: 3637e45 ("drm/amd/display: Fix wrong handling for AUX_DEFER case")
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Ray Wu <ray.wu@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -12854,7 +12854,8 @@ int amdgpu_dm_process_dmub_aux_transfer_sync(
 		/* The reply is stored in the top nibble of the command. */
 		payload->reply[0] = (adev->dm.dmub_notify->aux_reply.command >> 4) & 0xF;
 
-	if (!payload->write && p_notify->aux_reply.length)
+	/*write req may receive a byte indicating partially written number as well*/
+	if (p_notify->aux_reply.length)
 		memcpy(payload->data, p_notify->aux_reply.data,
 				p_notify->aux_reply.length);
 

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c

@@ -62,6 +62,7 @@ static ssize_t dm_dp_aux_transfer(struct drm_dp_aux *aux,
 	enum aux_return_code_type operation_result;
 	struct amdgpu_device *adev;
 	struct ddc_service *ddc;
+	uint8_t copy[16];
 
 	if (WARN_ON(msg->size > 16))
 		return -E2BIG;
@@ -77,6 +78,11 @@ static ssize_t dm_dp_aux_transfer(struct drm_dp_aux *aux,
 			(msg->request & DP_AUX_I2C_WRITE_STATUS_UPDATE) != 0;
 	payload.defer_delay = 0;
 
+	if (payload.write) {
+		memcpy(copy, msg->buffer, msg->size);
+		payload.data = copy;
+	}
+
 	result = dc_link_aux_transfer_raw(TO_DM_AUX(aux)->ddc_service, &payload,
 				      &operation_result);
 
@@ -100,9 +106,9 @@ static ssize_t dm_dp_aux_transfer(struct drm_dp_aux *aux,
 	 */
 	if (payload.write && result >= 0) {
 		if (result) {
-			/*one byte indicating partially written bytes. Force 0 to retry*/
+			/*one byte indicating partially written bytes*/
 			drm_info(adev_to_drm(adev), "amdgpu: AUX partially written\n");
-			result = 0;
+			result = payload.data[0];
 		} else if (!payload.reply[0])
 			/*I2C_ACK|AUX_ACK*/
 			result = msg->size;