drm/i915: add the FCLK case to intel_ddi_get_cdclk_freq

We already have code to disable LCPLL and switch to FCLK, so we need this too.
We still don't call the code to disable LCPLL, but we'll call it when we add
support for Package C8+.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -1139,10 +1139,13 @@ static void intel_disable_ddi(struct intel_encoder *intel_encoder)
 
 int intel_ddi_get_cdclk_freq(struct drm_i915_private *dev_priv)
 {
-	if (I915_READ(HSW_FUSE_STRAP) & HSW_CDCLK_LIMIT)
+	uint32_t lcpll = I915_READ(LCPLL_CTL);
+
+	if (lcpll & LCPLL_CD_SOURCE_FCLK)
+		return 800000;
+	else if (I915_READ(HSW_FUSE_STRAP) & HSW_CDCLK_LIMIT)
 		return 450000;
-	else if ((I915_READ(LCPLL_CTL) & LCPLL_CLK_FREQ_MASK) ==
-		 LCPLL_CLK_FREQ_450)
+	else if ((lcpll & LCPLL_CLK_FREQ_MASK) == LCPLL_CLK_FREQ_450)
 		return 450000;
 	else if (IS_ULT(dev_priv->dev))
 		return 337500;