[PATCH 5.3 130/197] drm/i915: Favor last VBT child device with conflicting AUX ch/DDC pin

[Greg Kroah-Hartman]

From: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>

commit 0336ab580878f4c5663dfa2b66095821fdc3e588 upstream.

The first come first served apporoach to handling the VBT
child device AUX ch conflicts has backfired. We have machines
in the wild where the VBT specifies both port A eDP and
port E DP (in that order) with port E being the real one.

So let's try to flip the preference around and let the last
child device win once again.

Cc: stable@xxxxxxxxxxxxxxx
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Tested-by: Masami Ichikawa <masami256@xxxxxxxxx>
Tested-by: Torsten <freedesktop201910@xxxxxxxx>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111966
Fixes: 36a0f92020dc ("drm/i915/bios: make child device order the priority order")
Signed-off-by: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20191011202030.8829-1-ville.syrjala@xxxxxxxxxxxxxxx
Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx>
(cherry picked from commit 41e35ffb380bde1379e4030bb5b2ac824d5139cf)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/display/intel_bios.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

--- a/drivers/gpu/drm/i915/display/intel_bios.c
+++ b/drivers/gpu/drm/i915/display/intel_bios.c
@@ -1269,7 +1269,7 @@ static void sanitize_ddc_pin(struct drm_
 		DRM_DEBUG_KMS("port %c trying to use the same DDC pin (0x%x) as port %c, "
 			      "disabling port %c DVI/HDMI support\n",
 			      port_name(port), info->alternate_ddc_pin,
-			      port_name(p), port_name(port));
+			      port_name(p), port_name(p));
 
 		/*
 		 * If we have multiple ports supposedly sharing the
@@ -1277,9 +1277,14 @@ static void sanitize_ddc_pin(struct drm_
 		 * port. Otherwise they share the same ddc bin and
 		 * system couldn't communicate with them separately.
 		 *
-		 * Give child device order the priority, first come first
-		 * served.
+		 * Give inverse child device order the priority,
+		 * last one wins. Yes, there are real machines
+		 * (eg. Asrock B250M-HDV) where VBT has both
+		 * port A and port E with the same AUX ch and
+		 * we must pick port E :(
 		 */
+		info = &dev_priv->vbt.ddi_port_info[p];
+
 		info->supports_dvi = false;
 		info->supports_hdmi = false;
 		info->alternate_ddc_pin = 0;
@@ -1315,7 +1320,7 @@ static void sanitize_aux_ch(struct drm_i
 		DRM_DEBUG_KMS("port %c trying to use the same AUX CH (0x%x) as port %c, "
 			      "disabling port %c DP support\n",
 			      port_name(port), info->alternate_aux_channel,
-			      port_name(p), port_name(port));
+			      port_name(p), port_name(p));
 
 		/*
 		 * If we have multiple ports supposedlt sharing the
@@ -1323,9 +1328,14 @@ static void sanitize_aux_ch(struct drm_i
 		 * port. Otherwise they share the same aux channel
 		 * and system couldn't communicate with them separately.
 		 *
-		 * Give child device order the priority, first come first
-		 * served.
+		 * Give inverse child device order the priority,
+		 * last one wins. Yes, there are real machines
+		 * (eg. Asrock B250M-HDV) where VBT has both
+		 * port A and port E with the same AUX ch and
+		 * we must pick port E :(
 		 */
+		info = &dev_priv->vbt.ddi_port_info[p];
+
 		info->supports_dp = false;
 		info->alternate_aux_channel = 0;
 	}