drm/i915: Enforce max hdisplay/hblank_start limits on HSW/BDW FDI

The PCH transcoder registers are only 12 bits wide for the hdisplay
and hblank_start values. On HSW/BDW the CPU side registers are 13
bits wide. intel_mode_valid() only checks against the higher limit
(since we don't know where the mode is to be used), so an extra
check is required against the FDI limits.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180615174406.12258-3-ville.syrjala@linux.intel.com
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

drivers/gpu/drm/i915/intel_crt.c

@@ -337,6 +337,10 @@ intel_crt_mode_valid(struct drm_connector *connector,
 	    (ironlake_get_lanes_required(mode->clock, 270000, 24) > 2))
 		return MODE_CLOCK_HIGH;
 
+	/* HSW/BDW FDI limited to 4k */
+	if (mode->hdisplay > 4096)
+		return MODE_H_ILLEGAL;
+
 	return MODE_OK;
 }
 
@@ -379,6 +383,11 @@ static bool hsw_crt_compute_config(struct intel_encoder *encoder,
 	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		return false;
 
+	/* HSW/BDW FDI limited to 4k */
+	if (adjusted_mode->crtc_hdisplay > 4096 ||
+	    adjusted_mode->crtc_hblank_start > 4096)
+		return false;
+
 	pipe_config->has_pch_encoder = true;
 
 	/* LPT FDI RX only supports 8bpc. */