[PATCH 11/32] drm/tegra: dp: Read AUX read interval from DPCD

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

Store the AUX read interval from DPCD, so that it can be used to wait
for the durations given in the specification during link training.

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 drivers/gpu/drm/tegra/dp.c | 31 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/tegra/dp.h | 11 +++++++++++
 2 files changed, 42 insertions(+)

diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c
index 2be0a47ecbec..757a0256592f 100644
--- a/drivers/gpu/drm/tegra/dp.c
+++ b/drivers/gpu/drm/tegra/dp.c
@@ -40,6 +40,8 @@ static void drm_dp_link_reset(struct drm_dp_link *link)
 	link->max_lanes = 0;
 
 	drm_dp_link_caps_reset(&link->caps);
+	link->aux_rd_interval.cr = 0;
+	link->aux_rd_interval.ce = 0;
 	link->edp = 0;
 
 	link->rate = 0;
@@ -60,6 +62,7 @@ static void drm_dp_link_reset(struct drm_dp_link *link)
 int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 {
 	u8 dpcd[DP_RECEIVER_CAP_SIZE], value;
+	unsigned int rd_interval;
 	int err;
 
 	drm_dp_link_reset(link);
@@ -90,6 +93,34 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 			link->edp = drm_dp_edp_revisions[value];
 	}
 
+	/*
+	 * The DPCD stores the AUX read interval in units of 4 ms. There are
+	 * two special cases:
+	 *
+	 *   1) if the TRAINING_AUX_RD_INTERVAL field is 0, the clock recovery
+	 *      and channel equalization should use 100 us or 400 us AUX read
+	 *      intervals, respectively
+	 *
+	 *   2) for DP v1.4 and above, clock recovery should always use 100 us
+	 *      AUX read intervals
+	 */
+	rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
+			   DP_TRAINING_AUX_RD_MASK;
+
+	if (rd_interval > 4) {
+		DRM_DEBUG_KMS("AUX interval %u out of range (max. 4)\n",
+			      rd_interval);
+		rd_interval = 4;
+	}
+
+	rd_interval *= 4 * USEC_PER_MSEC;
+
+	if (rd_interval == 0 || link->revision >= DP_DPCD_REV_14)
+		link->aux_rd_interval.cr = 100;
+
+	if (rd_interval == 0)
+		link->aux_rd_interval.ce = 400;
+
 	link->rate = link->max_rate;
 	link->lanes = link->max_lanes;
 
diff --git a/drivers/gpu/drm/tegra/dp.h b/drivers/gpu/drm/tegra/dp.h
index 681cbd0a0094..1fe2d4f45ba3 100644
--- a/drivers/gpu/drm/tegra/dp.h
+++ b/drivers/gpu/drm/tegra/dp.h
@@ -60,6 +60,7 @@ void drm_dp_link_caps_copy(struct drm_dp_link_caps *dest,
  * @max_rate: maximum clock rate supported on the link
  * @max_lanes: maximum number of lanes supported on the link
  * @caps: capabilities supported on the link (see &drm_dp_link_caps)
+ * @aux_rd_interval: AUX read interval to use for training (in microseconds)
  * @edp: eDP revision (0x11: eDP 1.1, 0x12: eDP 1.2, ...)
  * @rate: currently configured link rate
  * @lanes: currently configured number of lanes
@@ -70,6 +71,16 @@ struct drm_dp_link {
 	unsigned int max_lanes;
 
 	struct drm_dp_link_caps caps;
+
+	/**
+	 * @cr: clock recovery read interval
+	 * @ce: channel equalization read interval
+	 */
+	struct {
+		unsigned int cr;
+		unsigned int ce;
+	} aux_rd_interval;
+
 	unsigned char edp;
 
 	unsigned int rate;
-- 
2.23.0