drm/i915: Reject modeset if the dotclock is too high

Reject the modeset if the requested dotclock exceeds the maximum allowed
by the hardware. So far we've only checked this on gen2/3 while also
handling the double wide vs. single wide pipe selection. Extend the
check to all platforms since we have the max dotclock correctly
populated now across the board.

Testcase: igt/kms_invalid_dotclock
Cc: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1464114859-15610-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -6624,10 +6624,10 @@ static int intel_crtc_compute_config(struct intel_crtc *crtc,
 	struct drm_device *dev = crtc->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	const struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
+	int clock_limit = dev_priv->max_dotclk_freq;
 
-	/* FIXME should check pixel clock limits on all platforms */
 	if (INTEL_INFO(dev)->gen < 4) {
-		int clock_limit = dev_priv->max_cdclk_freq * 9 / 10;
+		clock_limit = dev_priv->max_cdclk_freq * 9 / 10;
 
 		/*
 		 * Enable double wide mode when the dot clock
@@ -6635,16 +6635,16 @@ static int intel_crtc_compute_config(struct intel_crtc *crtc,
 		 */
 		if (intel_crtc_supports_double_wide(crtc) &&
 		    adjusted_mode->crtc_clock > clock_limit) {
-			clock_limit *= 2;
+			clock_limit = dev_priv->max_dotclk_freq;
 			pipe_config->double_wide = true;
 		}
+	}
 
-		if (adjusted_mode->crtc_clock > clock_limit) {
-			DRM_DEBUG_KMS("requested pixel clock (%d kHz) too high (max: %d kHz, double wide: %s)\n",
-				      adjusted_mode->crtc_clock, clock_limit,
-				      yesno(pipe_config->double_wide));
-			return -EINVAL;
-		}
+	if (adjusted_mode->crtc_clock > clock_limit) {
+		DRM_DEBUG_KMS("requested pixel clock (%d kHz) too high (max: %d kHz, double wide: %s)\n",
+			      adjusted_mode->crtc_clock, clock_limit,
+			      yesno(pipe_config->double_wide));
+		return -EINVAL;
 	}
 
 	/*