[PATCH 07/12] drm/dp: Set channel coding on link configuration

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

Make use of ANSI 8B/10B channel coding if the DisplayPort sink supports
it.

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 12 +++++++++++-
 include/drm/drm_dp_helper.h     |  8 ++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 2c774ffa2943..0cf5b1c278ae 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -305,6 +305,7 @@ static void drm_dp_link_caps_reset(struct drm_dp_link_caps *caps)
 	caps->enhanced_framing = false;
 	caps->tps3_supported = false;
 	caps->fast_training = false;
+	caps->channel_coding = false;
 }
 
 void drm_dp_link_caps_copy(struct drm_dp_link_caps *dest,
@@ -313,6 +314,7 @@ void drm_dp_link_caps_copy(struct drm_dp_link_caps *dest,
 	dest->enhanced_framing = src->enhanced_framing;
 	dest->tps3_supported = src->tps3_supported;
 	dest->fast_training = src->fast_training;
+	dest->channel_coding = src->channel_coding;
 }
 
 static void drm_dp_link_reset(struct drm_dp_link *link)
@@ -359,6 +361,7 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 	link->caps.enhanced_framing = drm_dp_enhanced_frame_cap(values);
 	link->caps.tps3_supported = drm_dp_tps3_supported(values);
 	link->caps.fast_training = drm_dp_fast_training_cap(values);
+	link->caps.channel_coding = drm_dp_channel_coding_supported(values);
 
 	link->rate = link->max_rate;
 	link->lanes = link->max_lanes;
@@ -445,7 +448,7 @@ EXPORT_SYMBOL(drm_dp_link_power_down);
  */
 int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
 {
-	u8 values[2];
+	u8 values[2], value = 0;
 	int err;
 
 	values[0] = drm_dp_link_rate_to_bw_code(link->rate);
@@ -458,6 +461,13 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
 	if (err < 0)
 		return err;
 
+	if (link->caps.channel_coding)
+		value = DP_SET_ANSI_8B10B;
+
+	err = drm_dp_dpcd_writeb(aux, DP_MAIN_LINK_CHANNEL_CODING_SET, value);
+	if (err < 0)
+		return err;
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_link_configure);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index bf280a4230fa..201e654b2257 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -88,6 +88,7 @@
 # define DP_DETAILED_CAP_INFO_AVAILABLE	    (1 << 4) /* DPI */
 
 #define DP_MAIN_LINK_CHANNEL_CODING         0x006
+# define DP_CAP_ANSI_8B10B		    (1 << 0)
 
 #define DP_DOWN_STREAM_PORT_COUNT	    0x007
 # define DP_PORT_COUNT_MASK		    0x0f
@@ -652,6 +653,12 @@ drm_dp_fast_training_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 		(dpcd[DP_MAX_DOWNSPREAD] & DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
 }
 
+static inline bool
+drm_dp_channel_coding_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	return dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_8B10B;
+}
+
 /*
  * DisplayPort AUX channel
  */
@@ -766,6 +773,7 @@ struct drm_dp_link_caps {
 	bool enhanced_framing;
 	bool tps3_supported;
 	bool fast_training;
+	bool channel_coding;
 };
 
 void drm_dp_link_caps_copy(struct drm_dp_link_caps *dest,
-- 
2.5.0