drm/i915/dp_mst: Enable HBLANK expansion quirk for UHBR rates

Enabling the 5k@60Hz uncompressed mode on the MediaTek/Dell U3224KBA
monitor results in a blank screen, at least on MTL platforms on UHBR
link rates with some (<30) uncompressed bpp values. Enabling compression
fixes the problem, so do that for now. Windows enables DSC always if the
sink supports it and forcing it to enable the mode without compression
leads to the same problem above (which suggests a panel issue with
uncompressed mode).

The same 5k mode on non-UHBR link rates is not affected and lower
resolution modes are not affected either. The problem is similar to the
one fixed by the HBLANK expansion quirk on Synaptics hubs, with the
difference that the problematic mode has a longer HBLANK duration. Also
the monitor doesn't report supporting HBLANK expansion; either its
internal MST hub does the expansion internally - similarly to the
Synaptics hub - or the issue has another root cause, but still related
to the mode's short HBLANK duration. Enable the quirk for the monitor
adjusting the detection for the above differences.

v2: Rebase on drm_dp_128132b_supported() change.

Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Tested-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240417142217.457902-1-imre.deak@intel.com

1 files changed, 18 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 5f2217483a87..37ff5457d5d1 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -421,15 +421,22 @@ static int mode_hblank_period_ns(const struct drm_display_mode *mode)
 
 static bool
 hblank_expansion_quirk_needs_dsc(const struct intel_connector *connector,
-				 const struct intel_crtc_state *crtc_state)
+				 const struct intel_crtc_state *crtc_state,
+				 const struct link_config_limits *limits)
 {
 	const struct drm_display_mode *adjusted_mode =
 		&crtc_state->hw.adjusted_mode;
+	bool is_uhbr_sink = connector->mst_port &&
+			    drm_dp_128b132b_supported(connector->mst_port->dpcd);
+	int hblank_limit = is_uhbr_sink ? 500 : 300;
 
 	if (!connector->dp.dsc_hblank_expansion_quirk)
 		return false;
 
-	if (mode_hblank_period_ns(adjusted_mode) > 300)
+	if (is_uhbr_sink && !drm_dp_is_uhbr_rate(limits->max_rate))
+		return false;
+
+	if (mode_hblank_period_ns(adjusted_mode) > hblank_limit)
 		return false;
 
 	return true;
@@ -445,7 +452,7 @@ adjust_limits_for_dsc_hblank_expansion_quirk(const struct intel_connector *conne
 	const struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
 	int min_bpp_x16 = limits->link.min_bpp_x16;
 
-	if (!hblank_expansion_quirk_needs_dsc(connector, crtc_state))
+	if (!hblank_expansion_quirk_needs_dsc(connector, crtc_state, limits))
 		return true;
 
 	if (!dsc) {
@@ -1604,7 +1611,14 @@ static bool detect_dsc_hblank_expansion_quirk(const struct intel_connector *conn
 			      DP_DPCD_QUIRK_HBLANK_EXPANSION_REQUIRES_DSC))
 		return false;
 
-	if (!(dpcd[DP_RECEIVE_PORT_0_CAP_0] & DP_HBLANK_EXPANSION_CAPABLE))
+	/*
+	 * UHBR (MST sink) devices requiring this quirk don't advertise the
+	 * HBLANK expansion support. Presuming that they perform HBLANK
+	 * expansion internally, or are affected by this issue on modes with a
+	 * short HBLANK for other reasons.
+	 */
+	if (!drm_dp_128b132b_supported(dpcd) &&
+	    !(dpcd[DP_RECEIVE_PORT_0_CAP_0] & DP_HBLANK_EXPANSION_CAPABLE))
 		return false;
 
 	drm_dbg_kms(&i915->drm,