drm/i915: Also check for VGA converter in eDP probe

commit f76f83a83c8fdbb62acbf8bd945f10821768145b upstream.

Unfortunately even the HPD based detection added in
commit cfe5bdfb27fa ("drm/i915: Check HPD live state during eDP probe")
fails to detect that the VBT's eDP/DDI-A is a ghost on
Asus B360M-A (CFL+CNP). On that board eDP/DDI-A has its HPD
asserted despite nothing being actually connected there :(
The straps/fuses also indicate that the eDP port is present.

So if one boots with a VGA monitor connected the eDP probe will
mistake the DP->VGA converter hooked to DDI-E for an eDP panel
on DDI-A.

As a last resort check what kind of DP device we've detected,
and if it looks like a DP->VGA converter then conclude that
the eDP port should be ignored.

Cc: stable@vger.kernel.org
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9636
Fixes: cfe5bdfb27fa ("drm/i915: Check HPD live state during eDP probe")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231114142333.15799-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit fcd479a79120bf0cd507d85f898297a3b868dda6)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index b4583d1..119a4de 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -5517,8 +5517,7 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
         * (eg. Acer Chromebook C710), so we'll check it only if multiple
         * ports are attempting to use the same AUX CH, according to VBT.
         */
-       if (intel_bios_dp_has_shared_aux_ch(encoder->devdata) &&
-           !intel_digital_port_connected(encoder)) {
+       if (intel_bios_dp_has_shared_aux_ch(encoder->devdata)) {
                /*
                 * If this fails, presume the DPCD answer came
                 * from some other port using the same AUX CH.
@@ -5526,10 +5525,27 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
                 * FIXME maybe cleaner to check this before the
                 * DPCD read? Would need sort out the VDD handling...
                 */
-               drm_info(&dev_priv->drm,
-                        "[ENCODER:%d:%s] HPD is down, disabling eDP\n",
-                        encoder->base.base.id, encoder->base.name);
-               goto out_vdd_off;
+               if (!intel_digital_port_connected(encoder)) {
+                       drm_info(&dev_priv->drm,
+                                "[ENCODER:%d:%s] HPD is down, disabling eDP\n",
+                                encoder->base.base.id, encoder->base.name);
+                       goto out_vdd_off;
+               }
+
+               /*
+                * Unfortunately even the HPD based detection fails on
+                * eg. Asus B360M-A (CFL+CNP), so as a last resort fall
+                * back to checking for a VGA branch device. Only do this
+                * on known affected platforms to minimize false positives.
+                */
+               if (DISPLAY_VER(dev_priv) == 9 && drm_dp_is_branch(intel_dp->dpcd) &&
+                   (intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_TYPE_MASK) ==
+                   DP_DWN_STRM_PORT_TYPE_ANALOG) {
+                       drm_info(&dev_priv->drm,
+                                "[ENCODER:%d:%s] VGA converter detected, disabling eDP\n",
+                                encoder->base.base.id, encoder->base.name);
+                       goto out_vdd_off;
+               }
        }
 
        mutex_lock(&dev_priv->drm.mode_config.mutex);