drm/i915/skl: Derive the max CDCLK from DFSM

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

drivers/gpu/drm/i915/i915_reg.h

@@ -5761,6 +5761,13 @@ enum skl_disp_power_wells {
 #define HSW_NDE_RSTWRN_OPT	0x46408
 #define  RESET_PCH_HANDSHAKE_ENABLE	(1<<4)
 
+#define SKL_DFSM			0x51000
+#define SKL_DFSM_CDCLK_LIMIT_MASK	(3 << 23)
+#define SKL_DFSM_CDCLK_LIMIT_675	(0 << 23)
+#define SKL_DFSM_CDCLK_LIMIT_540	(1 << 23)
+#define SKL_DFSM_CDCLK_LIMIT_450	(2 << 23)
+#define SKL_DFSM_CDCLK_LIMIT_337_5	(3 << 23)
+
 #define FF_SLICE_CS_CHICKEN2			0x20e4
 #define  GEN9_TSG_BARRIER_ACK_DISABLE		(1<<8)
 

drivers/gpu/drm/i915/intel_display.c

@@ -5751,7 +5751,18 @@ static void intel_update_max_cdclk(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
-	if (IS_BROADWELL(dev))  {
+	if (IS_SKYLAKE(dev)) {
+		u32 limit = I915_READ(SKL_DFSM) & SKL_DFSM_CDCLK_LIMIT_MASK;
+
+		if (limit == SKL_DFSM_CDCLK_LIMIT_675)
+			dev_priv->max_cdclk_freq = 675000;
+		else if (limit == SKL_DFSM_CDCLK_LIMIT_540)
+			dev_priv->max_cdclk_freq = 540000;
+		else if (limit == SKL_DFSM_CDCLK_LIMIT_450)
+			dev_priv->max_cdclk_freq = 450000;
+		else
+			dev_priv->max_cdclk_freq = 337500;
+	} else if (IS_BROADWELL(dev))  {
 		/*
 		 * FIXME with extra cooling we can allow
 		 * 540 MHz for ULX and 675 Mhz for ULT.