drm/i915: Store max dotclock

Store max dotclock into dev_priv structure so we are able
to filter out the modes that are not supported by our
platforms.

V2:
- limit the max dot clock frequency to max CD clock frequency
  for the gen9 and above
- limit the max dot clock frequency to 90% of the max CD clock
  frequency for the older gens
- for Cherryview the max dot clock frequency is limited to 95%
  of the max CD clock frequency
- for gen2 and gen3 the max dot clock limit is set to 90% of the
  2X max CD clock frequency

V3:
- max_dotclk variable renamed as max_dotclk_freq in i915_drv.h
- in intel_compute_max_dotclk() the rounding method changed from
  round up to round down when computing max dotclock

V4:
- Haswell and Broadwell supports now dot clocks up to max CD clock
  frequency

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1792,6 +1792,7 @@ struct drm_i915_private {
 	unsigned int fsb_freq, mem_freq, is_ddr3;
 	unsigned int skl_boot_cdclk;
 	unsigned int cdclk_freq, max_cdclk_freq;
+	unsigned int max_dotclk_freq;
 	unsigned int hpll_freq;
 
 	/**

drivers/gpu/drm/i915/intel_display.c

@@ -5240,6 +5240,21 @@ static void modeset_update_crtc_power_domains(struct drm_atomic_state *state)
 			modeset_put_power_domains(dev_priv, put_domains[i]);
 }
 
+static int intel_compute_max_dotclk(struct drm_i915_private *dev_priv)
+{
+	int max_cdclk_freq = dev_priv->max_cdclk_freq;
+
+	if (INTEL_INFO(dev_priv)->gen >= 9 ||
+	    IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))
+		return max_cdclk_freq;
+	else if (IS_CHERRYVIEW(dev_priv))
+		return max_cdclk_freq*95/100;
+	else if (INTEL_INFO(dev_priv)->gen < 4)
+		return 2*max_cdclk_freq*90/100;
+	else
+		return max_cdclk_freq*90/100;
+}
+
 static void intel_update_max_cdclk(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -5279,8 +5294,13 @@ static void intel_update_max_cdclk(struct drm_device *dev)
 		dev_priv->max_cdclk_freq = dev_priv->cdclk_freq;
 	}
 
+	dev_priv->max_dotclk_freq = intel_compute_max_dotclk(dev_priv);
+
 	DRM_DEBUG_DRIVER("Max CD clock rate: %d kHz\n",
 			 dev_priv->max_cdclk_freq);
+
+	DRM_DEBUG_DRIVER("Max dotclock rate: %d kHz\n",
+			 dev_priv->max_dotclk_freq);
 }
 
 static void intel_update_cdclk(struct drm_device *dev)