[PATCH v4 2/5] drm/dp_helper: Always wait before retrying native aux transactions

[Lyude]

This is part of a patch series to migrate all of the workarounds for
commonly seen behavior from bad sinks in intel_dp_dpcd_read_wake() to
drm's DP helper.

Some sinks need some time during the process of resuming the system from
sleep before they're ready to handle transactions. While it would be
nice if they responded with NACKs in these scenarios, this isn't always
the case as a few sinks will just timeout on all of the transactions
they receive until they're ready.

Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_dp_helper.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index d1128fb..3b915e2 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -179,7 +179,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 {
 	struct drm_dp_aux_msg msg;
 	unsigned int retry;
-	int err;
+	int err = 0;
 
 	memset(&msg, 0, sizeof(msg));
 	msg.address = offset;
@@ -194,6 +194,10 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 	 * sufficient, bump to 32 which makes Dell 4k monitors happier.
 	 */
 	for (retry = 0; retry < 32; retry++) {
+		if (err != 0 && err != -ETIMEDOUT) {
+			usleep_range(AUX_RETRY_INTERVAL,
+				     AUX_RETRY_INTERVAL + 100);
+		}
 
 		mutex_lock(&aux->hw_mutex);
 		err = aux->transfer(aux, &msg);
@@ -205,7 +209,6 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 			return err;
 		}
 
-
 		switch (msg.reply & DP_AUX_NATIVE_REPLY_MASK) {
 		case DP_AUX_NATIVE_REPLY_ACK:
 			if (err < size)
@@ -214,10 +217,6 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 
 		case DP_AUX_NATIVE_REPLY_NACK:
 			return -EIO;
-
-		case DP_AUX_NATIVE_REPLY_DEFER:
-			usleep_range(AUX_RETRY_INTERVAL, AUX_RETRY_INTERVAL + 100);
-			break;
 		}
 	}
 
-- 
2.5.5