drm/i915: Validate mode against max. link data rate for DP MST

Not validating the mode rate against max. link rate results in not pruning
invalid modes. For e.g, a HBR2 5.4 Gbps 2-lane configuration does not
support 4k@60Hz. But, we do not reject this mode.

So, make use of the helpers in intel_dp to validate mode data rate against
max. link data rate of a configuration.

v3: Renamed local variables again for consistency (Manasi)
v2: Renamed mode data rate local variable to be more explanatory.

Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479243546-17189-1-git-send-email-dhinakaran.pandiyan@intel.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -161,14 +161,14 @@ static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
 	return min(source_max, sink_max);
 }
 
-static int
+int
 intel_dp_link_required(int pixel_clock, int bpp)
 {
 	/* pixel_clock is in kHz, divide bpp by 8 for bit to Byte conversion */
 	return DIV_ROUND_UP(pixel_clock * bpp, 8);
 }
 
-static int
+int
 intel_dp_max_data_rate(int max_link_clock, int max_lanes)
 {
 	/* max_link_clock is the link symbol clock (LS_Clk) in kHz and not the

drivers/gpu/drm/i915/intel_dp_mst.c

@@ -350,7 +350,17 @@ static enum drm_mode_status
 intel_dp_mst_mode_valid(struct drm_connector *connector,
 			struct drm_display_mode *mode)
 {
+	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 bpp = 24; /* MST uses fixed bpp */
+	int max_rate, mode_rate, max_lanes, max_link_clock;
+
+	max_link_clock = intel_dp_max_link_rate(intel_dp);
+	max_lanes = drm_dp_max_lane_count(intel_dp->dpcd);
+
+	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
+	mode_rate = intel_dp_link_required(mode->clock, bpp);
 
 	/* TODO - validate mode against available PBN for link */
 	if (mode->clock < 10000)
@@ -359,7 +369,7 @@ intel_dp_mst_mode_valid(struct drm_connector *connector,
 	if (mode->flags & DRM_MODE_FLAG_DBLCLK)
 		return MODE_H_ILLEGAL;
 
-	if (mode->clock > max_dotclk)
+	if (mode_rate > max_rate || mode->clock > max_dotclk)
 		return MODE_CLOCK_HIGH;
 
 	return MODE_OK;

drivers/gpu/drm/i915/intel_drv.h

@@ -1457,6 +1457,8 @@ bool intel_dp_read_dpcd(struct intel_dp *intel_dp);
 bool __intel_dp_read_desc(struct intel_dp *intel_dp,
 			  struct intel_dp_desc *desc);
 bool intel_dp_read_desc(struct intel_dp *intel_dp);
+int intel_dp_link_required(int pixel_clock, int bpp);
+int intel_dp_max_data_rate(int max_link_clock, int max_lanes);
 
 /* intel_dp_aux_backlight.c */
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector);