[PATCH v2 12/21] 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.

v2: use USEC_PER_MSEC instead of MSEC_PER_SEC for clarity

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 drivers/gpu/drm/drm_dp_helper.c |  3 +++
 include/drm/drm_dp_helper.h     | 35 +++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 5b36e8e39ca7..4112570dbe67 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -382,6 +382,7 @@ 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;
@@ -435,6 +436,8 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 			link->edp = edp_revs[value];
 	}
 
+	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 13c50e905205..e28b0941a8be 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -25,8 +25,11 @@
 
 #include <linux/delay.h>
 #include <linux/i2c.h>
+#include <linux/time64.h>
 #include <linux/types.h>
 
+#include <drm/drm_print.h>
+
 /*
  * Unless otherwise noted, all values are from the DP 1.1a spec.  Note that
  * DP and DPCD versions are independent.  Differences from 1.0 are not noted,
@@ -1229,6 +1232,36 @@ 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. If no
+ * read interval is specified and for DPCD v1.4 and later, the read interval
+ * is always 100 microseconds.
+ *
+ * Returns:
+ * The read AUX interval in microseconds.
+ */
+static inline unsigned int
+drm_dp_aux_rd_interval(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	unsigned int 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);
+
+	if (rd_interval > 0 && dpcd[DP_DPCD_REV] < DP_DPCD_REV_14)
+		rd_interval *= 4 * USEC_PER_MSEC;
+	else
+		rd_interval = 100;
+
+	return rd_interval;
+}
+
 /*
  * DisplayPort AUX channel
  */
@@ -1405,6 +1438,7 @@ 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
@@ -1415,6 +1449,7 @@ 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;
-- 
2.22.0