drm/i915: reject modes the LPT FDI receiver can't handle

More specifically, the LPT FDI RX only supports 8bpc and a maximum of
2 lanes, so anything above that won't work and should be rejected.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_crt.c

@@ -198,6 +198,11 @@ static int intel_crt_mode_valid(struct drm_connector *connector,
 	if (mode->clock > max_clock)
 		return MODE_CLOCK_HIGH;
 
+	/* The FDI receiver on LPT only supports 8bpc and only has 2 lanes. */
+	if (HAS_PCH_LPT(dev) &&
+	    (ironlake_get_lanes_required(mode->clock, 270000, 24) > 2))
+		return MODE_CLOCK_HIGH;
+
 	return MODE_OK;
 }
 

drivers/gpu/drm/i915/intel_display.c

@@ -5228,6 +5228,17 @@ static bool ironlake_check_fdi_lanes(struct intel_crtc *intel_crtc)
 	}
 }
 
+int ironlake_get_lanes_required(int target_clock, int link_bw, int bpp)
+{
+	/*
+	 * Account for spread spectrum to avoid
+	 * oversubscribing the link. Max center spread
+	 * is 2.5%; use 5% for safety's sake.
+	 */
+	u32 bps = target_clock * bpp * 21 / 20;
+	return bps / (link_bw * 8) + 1;
+}
+
 static void ironlake_set_m_n(struct drm_crtc *crtc,
 			     struct drm_display_mode *mode,
 			     struct drm_display_mode *adjusted_mode)
@@ -5281,15 +5292,9 @@ static void ironlake_set_m_n(struct drm_crtc *crtc,
 	else
 		target_clock = adjusted_mode->clock;
 
-	if (!lane) {
-		/*
-		 * Account for spread spectrum to avoid
-		 * oversubscribing the link. Max center spread
-		 * is 2.5%; use 5% for safety's sake.
-		 */
-		u32 bps = target_clock * intel_crtc->bpp * 21 / 20;
-		lane = bps / (link_bw * 8) + 1;
-	}
+	if (!lane)
+		lane = ironlake_get_lanes_required(target_clock, link_bw,
+						   intel_crtc->bpp);
 
 	intel_crtc->fdi_lanes = lane;
 

drivers/gpu/drm/i915/intel_drv.h

@@ -559,6 +559,7 @@ intel_pipe_to_cpu_transcoder(struct drm_i915_private *dev_priv,
 			     enum pipe pipe);
 extern void intel_wait_for_vblank(struct drm_device *dev, int pipe);
 extern void intel_wait_for_pipe_off(struct drm_device *dev, int pipe);
+extern int ironlake_get_lanes_required(int target_clock, int link_bw, int bpp);
 
 struct intel_load_detect_pipe {
 	struct drm_framebuffer *release_fb;