drm/i915: Store max cdclk value in dev_priv

Keep the cdclk maximum supported frequency around in dev_priv so that we
can verify certain things against it before actually changing the cdclk
frequency.

For now only VLV/CHV have support changing cdclk frequency, so other
plarforms get to assume cdclk is fixed.

v2: Rebased to the latest
v3: Rebased to the latest
v4: Fix for patch style problems

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/i915_drv.h

@@ -1743,7 +1743,7 @@ struct drm_i915_private {
 
 	unsigned int fsb_freq, mem_freq, is_ddr3;
 	unsigned int skl_boot_cdclk;
-	unsigned int cdclk_freq;
+	unsigned int cdclk_freq, max_cdclk_freq;
 	unsigned int hpll_freq;
 
 	/**

drivers/gpu/drm/i915/intel_display.c

@@ -5747,6 +5747,21 @@ static int valleyview_get_vco(struct drm_i915_private *dev_priv)
 	return vco_freq[hpll_freq] * 1000;
 }
 
+static void intel_update_max_cdclk(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (IS_VALLEYVIEW(dev)) {
+		dev_priv->max_cdclk_freq = 400000;
+	} else {
+		/* otherwise assume cdclk is fixed */
+		dev_priv->max_cdclk_freq = dev_priv->cdclk_freq;
+	}
+
+	DRM_DEBUG_DRIVER("Max CD clock rate: %d kHz\n",
+			 dev_priv->max_cdclk_freq);
+}
+
 static void intel_update_cdclk(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -5768,6 +5783,9 @@ static void intel_update_cdclk(struct drm_device *dev)
 		 */
 		I915_WRITE(GMBUSFREQ_VLV, DIV_ROUND_UP(dev_priv->cdclk_freq, 1000));
 	}
+
+	if (dev_priv->max_cdclk_freq == 0)
+		intel_update_max_cdclk(dev);
 }
 
 /* Adjust CDclk dividers to allow high res or save power if possible */
@@ -6610,7 +6628,7 @@ static int intel_crtc_compute_config(struct intel_crtc *crtc,
 
 	/* FIXME should check pixel clock limits on all platforms */
 	if (INTEL_INFO(dev)->gen < 4) {
-		int clock_limit = dev_priv->cdclk_freq;
+		int clock_limit = dev_priv->max_cdclk_freq;
 
 		/*
 		 * Enable pixel doubling when the dot clock