[Intel-gfx] [PATCH 2/2] drm/i915/mst: filter out the display mode exceed sink's capability

Lyude Paul lyude at redhat.com
Tue May 26 18:23:10 UTC 2020

From: Lee Shawn C <shawn.c.lee at intel.com>

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.

v2: Using mgr->base.lock to protect full_pbn.
v3: Add ctx lock.
* s/intel_dp_mst_mode_clock_exceed_pbn_bandwidth/
* Use the new drm_connector_helper_funcs.mode_valid_ctx to properly pipe
  down the drm_modeset_acquire_ctx that the probe helpers are using, so
  we can safely grab &mgr->base.lock without deadlocking

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>
Co-developed-by: Lyude Paul <lyude at redhat.com>
Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
Tested-by: Lee Shawn C <shawn.c.lee at intel.com>
Signed-off-by: Lyude Paul <lyude at redhat.com>
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 39 ++++++++++++++++++---
 1 file changed, 35 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 d18b406f2a7d2..cf052095ad785 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -610,15 +610,42 @@ static int intel_dp_mst_get_modes(struct drm_connector *connector)
 	return intel_dp_mst_get_ddc_modes(connector);
+static int
+intel_dp_mst_mode_clock_exceeds_pbn_bw(struct drm_connector *connector,
+				       struct drm_modeset_acquire_ctx *ctx,
+				       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;
+	int ret = MODE_OK;
+	if (!mgr)
+		return ret;
+	ret = drm_modeset_lock(&mgr->base.lock, ctx);
+	if (ret == -EDEADLK)
+		return ret;
+	if (port->full_pbn &&
+	    drm_dp_calc_pbn_mode(clock, bpp, false) > port->full_pbn)
+	return ret;
 static enum drm_mode_status
-intel_dp_mst_mode_valid(struct drm_connector *connector,
-			struct drm_display_mode *mode)
+intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
+			    struct drm_display_mode *mode,
+			    struct drm_modeset_acquire_ctx *ctx)
 	struct drm_i915_private *dev_priv = to_i915(connector->dev);
 	struct intel_connector *intel_connector = to_intel_connector(connector);
 	struct intel_dp *intel_dp = intel_connector->mst_port;
 	int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
 	int max_rate, mode_rate, max_lanes, max_link_clock;
+	int ret;
 	if (drm_connector_is_unregistered(connector))
 		return MODE_ERROR;
@@ -632,7 +659,11 @@ 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 */
+	ret = intel_dp_mst_mode_clock_exceeds_pbn_bw(connector, ctx,
+						     mode->clock, 24);
+	if (ret != MODE_OK)
+		return ret;
 	if (mode->clock < 10000)
 		return MODE_CLOCK_LOW;
@@ -671,7 +702,7 @@ intel_dp_mst_detect(struct drm_connector *connector,
 static const struct drm_connector_helper_funcs intel_dp_mst_connector_helper_funcs = {
 	.get_modes = intel_dp_mst_get_modes,
-	.mode_valid = intel_dp_mst_mode_valid,
+	.mode_valid_ctx = intel_dp_mst_mode_valid_ctx,
 	.atomic_best_encoder = intel_mst_atomic_best_encoder,
 	.atomic_check = intel_dp_mst_atomic_check,
 	.detect_ctx = intel_dp_mst_detect,

More information about the Intel-gfx mailing list