[RFC PATCH 1/2] drm/dp: Make number of AUX retries configurable by display drivers.

[Khaled Almahallawy]

The number of AUX retries specified in the DP specs is 7. Currently, to make Dell 4k monitors happier, the number of retries are 32.
i915 also retries 5 times (intel_dp_aux_xfer) which means in the case of AUX timeout we actually retries 32 * 5 = 160 times.

So making the number of aux retires a variable to allow for fine tuning and optimization of aux timing.

Signed-off-by: Khaled Almahallawy <khaled.almahallawy at intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 10 +++-------
 include/drm/drm_dp_helper.h     |  1 +
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index eedbb48815b7..8fdf57b4a06c 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -249,13 +249,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 
 	mutex_lock(&aux->hw_mutex);
 
-	/*
-	 * The specification doesn't give any recommendation on how often to
-	 * retry native transactions. We used to retry 7 times like for
-	 * aux i2c transactions but real world devices this wasn't
-	 * sufficient, bump to 32 which makes Dell 4k monitors happier.
-	 */
-	for (retry = 0; retry < 32; retry++) {
+	for (retry = 0; retry < aux->num_retries; retry++) {
 		if (ret != 0 && ret != -ETIMEDOUT) {
 			usleep_range(AUX_RETRY_INTERVAL,
 				     AUX_RETRY_INTERVAL + 100);
@@ -1744,6 +1738,8 @@ void drm_dp_aux_init(struct drm_dp_aux *aux)
 	aux->ddc.retries = 3;
 
 	aux->ddc.lock_ops = &drm_dp_i2c_lock_ops;
+	/*Still making the Dell 4k monitors happier*/
+	aux->num_retries = 32;
 }
 EXPORT_SYMBOL(drm_dp_aux_init);
 
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index edffd1dcca3e..16cbfc8f5e66 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1876,6 +1876,7 @@ struct drm_dp_aux {
 	struct mutex hw_mutex;
 	struct work_struct crc_work;
 	u8 crc_count;
+	int num_retries;
 	ssize_t (*transfer)(struct drm_dp_aux *aux,
 			    struct drm_dp_aux_msg *msg);
 	/**
-- 
2.25.1