[PATCH 06/17] drm/dp: Read fast training capability from link

[Thierry Reding <thierry.reding@xxxxxxxxx>]

From: Thierry Reding <treding@xxxxxxxxxx>

While probing the DisplayPort link, query the fast training capability.
If supported, drivers can use the fast link training sequence instead of
the more involved full link training sequence.

Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_dp_helper.c | 3 +++
 include/drm/drm_dp_helper.h     | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 982dd9febb1c..2d56aeda1b75 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -334,12 +334,14 @@ EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
 static void drm_dp_link_caps_reset(struct drm_dp_link_caps *caps)
 {
 	caps->enhanced_framing = false;
+	caps->fast_training = false;
 }
 
 void drm_dp_link_caps_copy(struct drm_dp_link_caps *dest,
 			   const struct drm_dp_link_caps *src)
 {
 	dest->enhanced_framing = src->enhanced_framing;
+	dest->fast_training = src->fast_training;
 }
 EXPORT_SYMBOL(drm_dp_link_caps_copy);
 
@@ -385,6 +387,7 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 	link->max_lanes = drm_dp_max_lane_count(values);
 
 	link->caps.enhanced_framing = drm_dp_enhanced_frame_cap(values);
+	link->caps.fast_training = drm_dp_fast_training_cap(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 85ff67958875..680d6719d463 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -976,6 +976,13 @@ drm_dp_is_branch(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 	return dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT;
 }
 
+static inline bool
+drm_dp_fast_training_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	return dpcd[DP_DPCD_REV] >= 0x11 &&
+		(dpcd[DP_MAX_DOWNSPREAD] & DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
+}
+
 /*
  * DisplayPort AUX channel
  */
@@ -1103,9 +1110,11 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
 /**
  * struct drm_dp_link_caps - DP link capabilities
  * @enhanced_framing: enhanced framing capability (mandatory as of DP 1.2)
+ * @fast_training: AUX CH handshake not required for link training
  */
 struct drm_dp_link_caps {
 	bool enhanced_framing;
+	bool fast_training;
 };
 
 void drm_dp_link_caps_copy(struct drm_dp_link_caps *dest,
-- 
2.15.1

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