[PATCH 11/12] drm/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/drm_dp_helper.c |  4 ++++
 include/drm/drm_dp_helper.h     | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 76ac68bc1042..da519acfeba7 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -339,6 +339,7 @@ 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 = 0;
 	link->edp = 0;
 
 	link->rate = 0;
@@ -392,6 +393,9 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 			link->edp = edp_revs[value];
 	}
 
+	/* DP_TRAINING_AUX_RD_INTERVAL is in units of 4 milliseconds */
+	link->aux_rd_interval = drm_dp_aux_rd_interval(values);
+
 	link->rate = link->max_rate;
 	link->lanes = link->max_lanes;
 
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 825aaf4e8c71..20ae0e413b64 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -678,6 +678,22 @@ drm_dp_alternate_scrambler_reset_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 			DP_ALTERNATE_SCRAMBLER_RESET_CAP;
 }
 
+/**
+ * drm_dp_read_aux_interval() - read the AUX read interval from the DPCD
+ * @dpcd: receiver capacity buffer
+ *
+ * Reads the AUX read interval (in microseconds) from the DPCD. Note that the
+ * TRAINING_AUX_RD_INTERVAL stores the value in units of 4 milliseconds.
+ *
+ * Returns:
+ * The read AUX interval in microseconds.
+ */
+static inline unsigned int
+drm_dp_aux_rd_interval(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	return dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4000;
+}
+
 /*
  * DisplayPort AUX channel
  */
@@ -805,6 +821,7 @@ struct drm_dp_link {
 	unsigned int max_lanes;
 
 	struct drm_dp_link_caps caps;
+	unsigned int aux_rd_interval;
 	unsigned char edp;
 
 	unsigned int rate;
-- 
2.5.0