drm/i915/bdw: get the correct LCPLL frequency on Broadwell

v2: Rebased onto Paulo's MHz->kHz change.

v3: Rebased on top of the Haswell pc8+ adjustements.

v4: Use the exact 337.5MHz clock, should have been done as part of v2.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> (v1)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -5315,6 +5315,9 @@
 #define  LCPLL_PLL_LOCK			(1<<30)
 #define  LCPLL_CLK_FREQ_MASK		(3<<26)
 #define  LCPLL_CLK_FREQ_450		(0<<26)
+#define  LCPLL_CLK_FREQ_54O_BDW		(1<<26)
+#define  LCPLL_CLK_FREQ_337_5_BDW	(2<<26)
+#define  LCPLL_CLK_FREQ_675_BDW		(3<<26)
 #define  LCPLL_CD_CLOCK_DISABLE		(1<<25)
 #define  LCPLL_CD2X_CLOCK_DISABLE	(1<<23)
 #define  LCPLL_POWER_DOWN_ALLOW		(1<<22)

drivers/gpu/drm/i915/intel_ddi.c

@@ -1158,18 +1158,29 @@ static void intel_disable_ddi(struct intel_encoder *intel_encoder)
 
 int intel_ddi_get_cdclk_freq(struct drm_i915_private *dev_priv)
 {
+	struct drm_device *dev = dev_priv->dev;
 	uint32_t lcpll = I915_READ(LCPLL_CTL);
+	uint32_t freq = lcpll & LCPLL_CLK_FREQ_MASK;
 
-	if (lcpll & LCPLL_CD_SOURCE_FCLK)
+	if (lcpll & LCPLL_CD_SOURCE_FCLK) {
 		return 800000;
-	else if (I915_READ(HSW_FUSE_STRAP) & HSW_CDCLK_LIMIT)
+	} else if (I915_READ(HSW_FUSE_STRAP) & HSW_CDCLK_LIMIT) {
 		return 450000;
-	else if ((lcpll & LCPLL_CLK_FREQ_MASK) == LCPLL_CLK_FREQ_450)
+	} else if (freq == LCPLL_CLK_FREQ_450) {
 		return 450000;
-	else if (IS_ULT(dev_priv->dev))
-		return 337500;
-	else
-		return 540000;
+	} else if (IS_HASWELL(dev)) {
+		if (IS_ULT(dev))
+			return 337500;
+		else
+			return 540000;
+	} else {
+		if (freq == LCPLL_CLK_FREQ_54O_BDW)
+			return 540000;
+		else if (freq == LCPLL_CLK_FREQ_337_5_BDW)
+			return 337500;
+		else
+			return 675000;
+	}
 }
 
 void intel_ddi_pll_init(struct drm_device *dev)