[Intel-gfx] [PATCH] drm/i915/mst: filter out the display mode exceed sink's capability

[Lee Shawn C]

So far, max dot clock rate for MST mode rely on physcial
bandwidth limitation. It would caused compatibility issue
if source display resolution exceed MST hub output ability.

For example, source DUT had DP 1.2 output capability.
And MST docking just support HDMI 1.4 spec. When a HDMI 2.0
monitor connected. Source would retrieve EDID from external
and get max resolution 4k at 60fps. DP 1.2 can support 4K at 60fps
because it did not surpass DP physical bandwidth limitation.
Do modeset to 4k at 60fps, source output display data but MST
docking can't output HDMI properly due to this resolution
already over HDMI 1.4 spec.

Refer to commit <fcf463807596> ("drm/dp_mst: Use full_pbn
instead of available_pbn for bandwidth checks").
Source driver should refer to full_pbn to evaluate sink
output capability. And filter out the resolution surpass
sink output limitation.

Cc: Manasi Navare <manasi.d.navare at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Cc: Cooper Chiou <cooper.chiou at intel.com>
Cc: Lyude Paul <lyude at redhat.com>
Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 24 ++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 61605eb8c2af..68697f463dab 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -609,6 +609,26 @@ static int intel_dp_mst_get_modes(struct drm_connector *connector)
 	return intel_dp_mst_get_ddc_modes(connector);
 }
 
+static bool
+intel_dp_mst_mode_clock_exceed_pbn_bandwidth(struct drm_connector *connector, int clock, int bpp)
+{
+	struct intel_connector *intel_connector = to_intel_connector(connector);
+	struct intel_dp *intel_dp = intel_connector->mst_port;
+	struct drm_dp_mst_topology_mgr *mgr = &intel_dp->mst_mgr;
+	struct drm_dp_mst_port *port = (to_intel_connector(connector))->port;
+	bool ret = false;
+
+	if (!mgr)
+		return ret;
+
+	mutex_lock(&mgr->lock);
+	if (port->full_pbn)
+		ret = (drm_dp_calc_pbn_mode(clock, bpp, false) > port->full_pbn);
+	mutex_unlock(&mgr->lock);
+
+	return ret;
+}
+
 static enum drm_mode_status
 intel_dp_mst_mode_valid(struct drm_connector *connector,
 			struct drm_display_mode *mode)
@@ -631,7 +651,9 @@ intel_dp_mst_mode_valid(struct drm_connector *connector,
 	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
 	mode_rate = intel_dp_link_required(mode->clock, 18);
 
-	/* TODO - validate mode against available PBN for link */
+	if (intel_dp_mst_mode_clock_exceed_pbn_bandwidth(connector, mode->clock, 24))
+		return MODE_CLOCK_HIGH;
+
 	if (mode->clock < 10000)
 		return MODE_CLOCK_LOW;
 
-- 
2.17.1