[4/5] drm: Fix for DP CTS test 4.2.2.5 - I2C DEFER handling

Submitted by Todd Previte on April 18, 2015, 7:04 a.m.

Details

Message ID 1429340659-14369-5-git-send-email-tprevite@gmail.com
State New
Headers show

Not browsing as part of any series.

Commit Message

Todd Previte April 18, 2015, 7:04 a.m.
For test 4.2.2.5 to pass per the Link CTS Core 1.2 rev1.1 spec, the source
device must attempt at least 7 times to read the EDID when it receives an
I2C defer. The normal DRM code makes only 7 retries, regardless of whether
or not the response is a native defer or an I2C defer. Test 4.2.2.5 fails
since there are native defers interspersed with the I2C defers which
results in less than 7 EDID read attempts.

The solution is to add the numer of defers to the retry counter when an I2C
DEFER is returned such that another read attempt will be made. This situation
should normally only occur in compliance testing, however, as a worse case
real-world scenario, it would result in 13 attempts ( 6 native defers, 7 I2C
defers) for a single transaction to complete. The net result is a slightly
slower response to an EDID read that shouldn't significantly impact overall
performance.

V2:
- Added a check on the number of I2C Defers to limit the number
  of times that the retries variable will be decremented. This
  is to address review feedback regarding possible infinite loops
  from misbehaving sink devices.
V3:
- Fixed the limit value to 7 instead of 8 to get the correct retry
  count.
- Combined the increment of the defer count into the if-statement
V4:
- Removed i915 tag from subject as the patch is not i915-specific
V5:
- Updated the for-loop to add the number of i2c defers to the retry
  counter such that the correct number of retry attempts will be
  made

Signed-off-by: Todd Previte <tprevite@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 575172e..80a02a4 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -432,7 +432,7 @@  static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
  */
 static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 {
-	unsigned int retry;
+	unsigned int retry, defer_i2c;
 	int ret;
 
 	/*
@@ -440,7 +440,7 @@  static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 	 * is required to retry at least seven times upon receiving AUX_DEFER
 	 * before giving up the AUX transaction.
 	 */
-	for (retry = 0; retry < 7; retry++) {
+	for (retry = 0, defer_i2c = 0; retry < (7 + defer_i2c); retry++) {
 		mutex_lock(&aux->hw_mutex);
 		ret = aux->transfer(aux, msg);
 		mutex_unlock(&aux->hw_mutex);
@@ -499,7 +499,13 @@  static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 
 		case DP_AUX_I2C_REPLY_DEFER:
 			DRM_DEBUG_KMS("I2C defer\n");
+			/* DP Compliance Test 4.2.2.5 Requirement:
+			 * Must have at least 7 retries for I2C defers on the
+			 * transaction to pass this test
+			 */
 			aux->i2c_defer_count++;
+			if (defer_i2c < 7)
+				defer_i2c++;
 			usleep_range(400, 500);
 			continue;
 

Comments

On Sat, Apr 18, 2015 at 12:04:18AM -0700, Todd Previte wrote:
> For test 4.2.2.5 to pass per the Link CTS Core 1.2 rev1.1 spec, the source
> device must attempt at least 7 times to read the EDID when it receives an
> I2C defer. The normal DRM code makes only 7 retries, regardless of whether
> or not the response is a native defer or an I2C defer. Test 4.2.2.5 fails
> since there are native defers interspersed with the I2C defers which
> results in less than 7 EDID read attempts.
> 
> The solution is to add the numer of defers to the retry counter when an I2C
> DEFER is returned such that another read attempt will be made. This situation
> should normally only occur in compliance testing, however, as a worse case
> real-world scenario, it would result in 13 attempts ( 6 native defers, 7 I2C
> defers) for a single transaction to complete. The net result is a slightly
> slower response to an EDID read that shouldn't significantly impact overall
> performance.
> 
> V2:
> - Added a check on the number of I2C Defers to limit the number
>   of times that the retries variable will be decremented. This
>   is to address review feedback regarding possible infinite loops
>   from misbehaving sink devices.
> V3:
> - Fixed the limit value to 7 instead of 8 to get the correct retry
>   count.
> - Combined the increment of the defer count into the if-statement
> V4:
> - Removed i915 tag from subject as the patch is not i915-specific
> V5:
> - Updated the for-loop to add the number of i2c defers to the retry
>   counter such that the correct number of retry attempts will be
>   made
> 
> Signed-off-by: Todd Previte <tprevite@gmail.com>
> Cc: dri-devel@lists.freedesktop.org
> Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

Applied to topic/drm-misc.
-Daniel

> ---
>  drivers/gpu/drm/drm_dp_helper.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 575172e..80a02a4 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -432,7 +432,7 @@ static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
>   */
>  static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  {
> -	unsigned int retry;
> +	unsigned int retry, defer_i2c;
>  	int ret;
>  
>  	/*
> @@ -440,7 +440,7 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  	 * is required to retry at least seven times upon receiving AUX_DEFER
>  	 * before giving up the AUX transaction.
>  	 */
> -	for (retry = 0; retry < 7; retry++) {
> +	for (retry = 0, defer_i2c = 0; retry < (7 + defer_i2c); retry++) {
>  		mutex_lock(&aux->hw_mutex);
>  		ret = aux->transfer(aux, msg);
>  		mutex_unlock(&aux->hw_mutex);
> @@ -499,7 +499,13 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  
>  		case DP_AUX_I2C_REPLY_DEFER:
>  			DRM_DEBUG_KMS("I2C defer\n");
> +			/* DP Compliance Test 4.2.2.5 Requirement:
> +			 * Must have at least 7 retries for I2C defers on the
> +			 * transaction to pass this test
> +			 */
>  			aux->i2c_defer_count++;
> +			if (defer_i2c < 7)
> +				defer_i2c++;
>  			usleep_range(400, 500);
>  			continue;
>  
> -- 
> 1.9.1
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel