drm/i915/skl: CD clock back calculation for SKL

Determine programmed cd clock for SKL.

v2: Fix the LCPLL1 enable warning logic

v3: Rebase over the hsw pll rework.

v4: Rebase on top of the per-platform split (Damien)

v5: Modified as per review comments from Paulo

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Satheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -1259,6 +1259,54 @@ static void intel_disable_ddi(struct intel_encoder *intel_encoder)
 	}
 }
 
+static int skl_get_cdclk_freq(struct drm_i915_private *dev_priv)
+{
+	uint32_t lcpll1 = I915_READ(LCPLL1_CTL);
+	uint32_t cdctl = I915_READ(CDCLK_CTL);
+	uint32_t linkrate;
+
+	if (!(lcpll1 & LCPLL_PLL_ENABLE)) {
+		WARN(1, "LCPLL1 not enabled\n");
+		return 24000; /* 24MHz is the cd freq with NSSC ref */
+	}
+
+	if ((cdctl & CDCLK_FREQ_SEL_MASK) == CDCLK_FREQ_540)
+		return 540000;
+
+	linkrate = (I915_READ(DPLL_CTRL1) &
+		    DPLL_CRTL1_LINK_RATE_MASK(SKL_DPLL0)) >> 1;
+
+	if (linkrate == DPLL_CRTL1_LINK_RATE_2160 ||
+	    linkrate == DPLL_CRTL1_LINK_RATE_1080) {
+		/* vco 8640 */
+		switch (cdctl & CDCLK_FREQ_SEL_MASK) {
+		case CDCLK_FREQ_450_432:
+			return 432000;
+		case CDCLK_FREQ_337_308:
+			return 308570;
+		case CDCLK_FREQ_675_617:
+			return 617140;
+		default:
+			WARN(1, "Unknown cd freq selection\n");
+		}
+	} else {
+		/* vco 8100 */
+		switch (cdctl & CDCLK_FREQ_SEL_MASK) {
+		case CDCLK_FREQ_450_432:
+			return 450000;
+		case CDCLK_FREQ_337_308:
+			return 337500;
+		case CDCLK_FREQ_675_617:
+			return 675000;
+		default:
+			WARN(1, "Unknown cd freq selection\n");
+		}
+	}
+
+	/* error case, do as if DPLL0 isn't enabled */
+	return 24000;
+}
+
 static int bdw_get_cdclk_freq(struct drm_i915_private *dev_priv)
 {
 	uint32_t lcpll = I915_READ(LCPLL_CTL);
@@ -1300,6 +1348,9 @@ int intel_ddi_get_cdclk_freq(struct drm_i915_private *dev_priv)
 {
 	struct drm_device *dev = dev_priv->dev;
 
+	if (IS_SKYLAKE(dev))
+		return skl_get_cdclk_freq(dev_priv);
+
 	if (IS_BROADWELL(dev))
 		return bdw_get_cdclk_freq(dev_priv);
 
@@ -1368,19 +1419,25 @@ void intel_ddi_pll_init(struct drm_device *dev)
 
 	hsw_shared_dplls_init(dev_priv);
 
-	/* The LCPLL register should be turned on by the BIOS. For now let's
-	 * just check its state and print errors in case something is wrong.
-	 * Don't even try to turn it on.
-	 */
-
 	DRM_DEBUG_KMS("CDCLK running at %dKHz\n",
 		      intel_ddi_get_cdclk_freq(dev_priv));
 
-	if (val & LCPLL_CD_SOURCE_FCLK)
-		DRM_ERROR("CDCLK source is not LCPLL\n");
+	if (IS_SKYLAKE(dev)) {
+		if (!(I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE))
+			DRM_ERROR("LCPLL1 is disabled\n");
+	} else {
+		/*
+		 * The LCPLL register should be turned on by the BIOS. For now
+		 * let's just check its state and print errors in case
+		 * something is wrong.  Don't even try to turn it on.
+		 */
+
+		if (val & LCPLL_CD_SOURCE_FCLK)
+			DRM_ERROR("CDCLK source is not LCPLL\n");
 
-	if (val & LCPLL_PLL_DISABLE)
-		DRM_ERROR("LCPLL is disabled\n");
+		if (val & LCPLL_PLL_DISABLE)
+			DRM_ERROR("LCPLL is disabled\n");
+	}
 }
 
 void intel_ddi_prepare_link_retrain(struct drm_encoder *encoder)