[RFC 01/13] drm/dp: Read fast training capability from link

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

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 at nvidia.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 5 ++++-
 include/drm/drm_dp_helper.h     | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 80a02a412607..bf480a08d7f9 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -295,7 +295,7 @@ EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
  */
 int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 {
-	u8 values[3];
+	u8 values[4];
 	int err;
 
 	memset(link, 0, sizeof(*link));
@@ -311,6 +311,9 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 	if (values[2] & DP_ENHANCED_FRAME_CAP)
 		link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING;
 
+	if (values[3] & DP_NO_AUX_HANDSHAKE_LINK_TRAINING)
+		link->capabilities |= DP_LINK_CAP_FAST_TRAINING;
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_link_probe);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 94898f6ea02a..61c0518704a3 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -742,6 +742,7 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
  * DisplayPort link
  */
 #define DP_LINK_CAP_ENHANCED_FRAMING (1 << 0)
+#define DP_LINK_CAP_FAST_TRAINING (1 << 1)
 
 struct drm_dp_link {
 	unsigned char revision;
-- 
2.4.5