drm/radeon: Prevent hdmi deep color if max_tmds_clock is undefined.

HDMI spec requires a valid max_tmds_clock from edid for hdmi
deep color modes. If a sink violates this, disable deep color.

Also add a hint to user about the deep_color module parameter if
deep color is disabled due to that.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c b/drivers/gpu/drm/radeon/radeon_connectors.c
index 19ad4fb0a610..300c4b3d4669 100644
--- a/drivers/gpu/drm/radeon/radeon_connectors.c
+++ b/drivers/gpu/drm/radeon/radeon_connectors.c
@@ -197,10 +197,19 @@ int radeon_get_monitor_bpc(struct drm_connector *connector)
                                                   connector->name, bpc);
                         }
                 }
+                else if (bpc > 8) {
+                        /* max_tmds_clock missing, but hdmi spec mandates it for deep color. */
+                        DRM_DEBUG("%s: Required max tmds clock for HDMI deep color missing. Using 8 bpc.\n",
+                                          connector->name);
+                        bpc = 8;
+                }
         }
 
-        if ((radeon_deep_color == 0) && (bpc > 8))
+        if ((radeon_deep_color == 0) && (bpc > 8)) {
+                DRM_DEBUG("%s: Deep color disabled. Set radeon module param deep_color=1 to enable.\n",
+                                  connector->name);
                 bpc = 8;
+        }
 
         DRM_DEBUG("%s: Display bpc=%d, returned bpc=%d\n",
                           connector->name, connector->display_info.bpc, bpc);