[PATCH 1/2] drm/dp: Correct Write_Status_Update_Request handling

[Wayne Lin]

[Why]
Notice few problems under I2C-write-over-Aux with
Write_Status_Update_Request flag set cases:

- I2C-write-over-Aux request with
  Write_Status_Update_Request flag set won't get sent
  upon the reply of I2C_ACK|AUX_ACK followed by “M”
  Value. Now just set the flag but won't send out

- The I2C-over-Aux request command with
  Write_Status_Update_Request flag set is incorrect.
  Should be "SYNC->COM3:0 (= 0110)|0000-> 0000|0000->
  0|7-bit I2C address (the same as the last)-> STOP->".
  Address only transaction without length and data.

- Upon I2C_DEFER|AUX_ACK Reply for I2C-read-over-Aux,
  soure should repeat the identical I2C-read-over-AUX
  transaction with the same LEN value. Not with
  Write_Status_Update_Request set.

[How]
Refer to DP v2.1: 2.11.7.1.5.3 & 2.11.7.1.5.4
- Clean aux msg buffer and size when constructing
  write status update request.

- Send out Write_Status_Update_Request upon reply of
  I2C_ACK|AUX_ACK followed by “M”

- Send Write_Status_Update_Request upon I2C_DEFER|AUX_ACK
  reply only when the request is I2C-write-over-Aux.

Fixes: 68ec2a2a2481 ("drm/dp: Use I2C_WRITE_STATUS_UPDATE to drain partial I2C_WRITE requests")
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Mario Limonciello <mario.limonciello at amd.com>
Cc: Harry Wentland <harry.wentland at amd.com>
Cc: stable at vger.kernel.org
Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
---
 drivers/gpu/drm/display/drm_dp_helper.c | 27 +++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index 6ee51003de3c..28f0708c3b27 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -1631,6 +1631,12 @@ static void drm_dp_i2c_msg_write_status_update(struct drm_dp_aux_msg *msg)
 		msg->request &= DP_AUX_I2C_MOT;
 		msg->request |= DP_AUX_I2C_WRITE_STATUS_UPDATE;
 	}
+
+	/*
+	 * Address only transaction
+	 */
+	msg->buffer = NULL;
+	msg->size = 0;
 }
 
 #define AUX_PRECHARGE_LEN 10 /* 10 to 16 */
@@ -1797,10 +1803,22 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 		case DP_AUX_I2C_REPLY_ACK:
 			/*
 			 * Both native ACK and I2C ACK replies received. We
-			 * can assume the transfer was successful.
+			 * can't assume the transfer was completed. Both I2C
+			 * WRITE/READ request may get I2C ack reply with partially
+			 * completion. We have to continue to poll for the
+			 * completion of the request.
 			 */
-			if (ret != msg->size)
-				drm_dp_i2c_msg_write_status_update(msg);
+			if (ret != msg->size) {
+				drm_dbg_kms(aux->drm_dev,
+					    "%s: I2C partially ack (result=%d, size=%zu)\n",
+					    aux->name, ret, msg->size);
+				if (!(msg->request & DP_AUX_I2C_READ)) {
+					usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
+					drm_dp_i2c_msg_write_status_update(msg);
+				}
+
+				continue;
+			}
 			return ret;
 
 		case DP_AUX_I2C_REPLY_NACK:
@@ -1819,7 +1837,8 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 			if (defer_i2c < 7)
 				defer_i2c++;
 			usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
-			drm_dp_i2c_msg_write_status_update(msg);
+			if (!(msg->request & DP_AUX_I2C_READ))
+				drm_dp_i2c_msg_write_status_update(msg);
 
 			continue;
 
-- 
2.43.0