[PATCH 2/2] drm/dp: Add handling for partially read under I2-readC-over-AUX

[Wayne Lin]

[Why]
There is no handling for I2C-read-over-AUX when receive reply of
I2C_ACK|AUX_ACK followed by the total number of data bytes Fewer
than LEN + 1

[How]
Refer to DP v2.1: 2.11.7.1.6.3 & 2.11.7.1.6.4, repeat the identical
I2C-read-over-AUX transaction with the updated LEN value equal to
the original LEN value minus the total number of data bytes received
so far.

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 | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index 28f0708c3b27..938214a980a9 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -1812,10 +1812,11 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 				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);
+				usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
+				if (msg->request & DP_AUX_I2C_READ)
+					msg->size -= ret;
+				else
 					drm_dp_i2c_msg_write_status_update(msg);
-				}
 
 				continue;
 			}
-- 
2.43.0