drm/dp: Add DP_DPCD_QUIRK_NO_SINK_COUNT

CH7511 eDP->LVDS bridge doesn't seem to set SINK_COUNT properly
causing i915 to detect it as disconnected. Add a quirk to ignore
SINK_COUNT on these devices.

Cc: David S. <david@majinbuu.com>
Cc: Peteris Rudzusiks <peteris.rudzusiks@gmail.com>
Tested-by: Peteris Rudzusiks <peteris.rudzusiks@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105406
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528140650.19230-1-ville.syrjala@linux.intel.com
Acked-by: Jani Nikula <jani.nikula@intel.com> #irc

drivers/gpu/drm/drm_dp_helper.c

@@ -1280,7 +1280,9 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
 	/* LG LP140WF6-SPM1 eDP panel */
 	{ OUI(0x00, 0x22, 0xb9), DEVICE_ID('s', 'i', 'v', 'a', 'r', 'T'), false, BIT(DP_DPCD_QUIRK_CONSTANT_N) },
 	/* Apple panels need some additional handling to support PSR */
-	{ OUI(0x00, 0x10, 0xfa), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_NO_PSR) }
+	{ OUI(0x00, 0x10, 0xfa), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_NO_PSR) },
+	/* CH7511 seems to leave SINK_COUNT zeroed */
+	{ OUI(0x00, 0x00, 0x00), DEVICE_ID('C', 'H', '7', '5', '1', '1'), false, BIT(DP_DPCD_QUIRK_NO_SINK_COUNT) },
 };
 
 #undef OUI

include/drm/drm_dp_helper.h

@@ -1414,6 +1414,13 @@ enum drm_dp_quirk {
 	 * driver still need to implement proper handling for such device.
 	 */
 	DP_DPCD_QUIRK_NO_PSR,
+	/**
+	 * @DP_DPCD_QUIRK_NO_SINK_COUNT:
+	 *
+	 * The device does not set SINK_COUNT to a non-zero value.
+	 * The driver should ignore SINK_COUNT during detection.
+	 */
+	DP_DPCD_QUIRK_NO_SINK_COUNT,
 };
 
 /**