[RFC 02/13] 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 | 16 ++++++++++++++--
 include/drm/drm_dp_helper.h     |  2 ++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index bf480a08d7f9..c48addaf4301 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[4];
+	u8 values[7];
 	int err;
 
 	memset(link, 0, sizeof(*link));
@@ -314,6 +314,9 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 	if (values[3] & DP_NO_AUX_HANDSHAKE_LINK_TRAINING)
 		link->capabilities |= DP_LINK_CAP_FAST_TRAINING;
 
+	if (values[6] & DP_SET_ANSI_8B10B)
+		link->capabilities |= DP_LINK_CAP_ANSI_8B10B;
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_link_probe);
@@ -396,7 +399,7 @@ 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);
@@ -409,6 +412,15 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
 	if (err < 0)
 		return err;
 
+	if (link->capabilities & DP_LINK_CAP_ANSI_8B10B)
+		value = DP_SET_ANSI_8B10B;
+	else
+		value = 0;
+
+	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 61c0518704a3..83be142395ff 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_CODING_ANSI_8B10B		    (1 << 0)
 
 #define DP_DOWN_STREAM_PORT_COUNT	    0x007
 # define DP_PORT_COUNT_MASK		    0x0f
@@ -743,6 +744,7 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
  */
 #define DP_LINK_CAP_ENHANCED_FRAMING (1 << 0)
 #define DP_LINK_CAP_FAST_TRAINING (1 << 1)
+#define DP_LINK_CAP_ANSI_8B10B (1 << 2)
 
 struct drm_dp_link {
 	unsigned char revision;
-- 
2.4.5