[Intel-gfx] [PATCH] drm/i915/dp: set fail-safe mode if EDID corrupt

[Lee Shawn C]

According to chapter 5.1.1.2 in DP spec. When the Sink
device capability is unknown, for example due to corruption
of an EDID. The Source device may fall back to a set of
fall-back video timing formats its choice. When none of
the fall-back video timing formats is acceptable, the
Source device must fall back to the fail safe mode,
which is 640 x 480 at 60Hz.

This change set source driver output fail-safe mode automatically
if EDID corrupt. It may also benefit link layer compliance
test case "4.2.2.6  EDID Corruption Detection".

Cc: Manasi Navare <manasi.d.navare at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Cooper Chiou <cooper.chiou at intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index c27d3e7ac219..7e072db4a530 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -5659,9 +5659,18 @@ intel_dp_get_edid(struct intel_dp *intel_dp)
 			return NULL;
 
 		return drm_edid_duplicate(intel_connector->edid);
-	} else
-		return drm_get_edid(&intel_connector->base,
+	} else {
+		struct edid *edid;
+
+		edid = drm_get_edid(&intel_connector->base,
 				    &intel_dp->aux.ddc);
+
+		if (intel_connector->base.edid_corrupt || !edid)
+			if (drm_add_modes_noedid(&intel_connector->base, 640, 480))
+				drm_set_preferred_mode(&intel_connector->base, 640, 480);
+
+		return edid;
+	}
 }
 
 static void
-- 
2.17.1