drm/i915/cnl: Implement .get_display_clock_speed() for CNL

Add support for reading out the cdclk frequency from the hardware on
CNL. Very similar to BXT, with a few new twists and turns:
* the PLL is now called CDCLK PLL, not DE PLL
* reference clock can be 24 MHz in addition to the 19.2 MHz BXT had
* the ratio now lives in the PLL enable register
* Only 1x and 2x CD2X dividers are supported

v2: Deal with PLL lock bit the same way as BXT/SKL do now
v3: DSSM refclk indicator is bit 31 not 24 (Ander)
v4: Rebased by Rodrigo after Ville's cdclk rework.
v5: Set cdclk to the ref clock as previous platforms. (Imre)
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1497047175-27250-1-git-send-email-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -6550,6 +6550,9 @@ enum {
 #define SKL_DFSM_PIPE_B_DISABLE		(1 << 21)
 #define SKL_DFSM_PIPE_C_DISABLE		(1 << 28)
 
+#define SKL_DSSM			_MMIO(0x51004)
+#define CNL_DSSM_CDCLK_PLL_REFCLK_24MHz	(1 << 31)
+
 #define GEN7_FF_SLICE_CS_CHICKEN1	_MMIO(0x20e0)
 #define   GEN9_FFSC_PERCTX_PREEMPT_CTRL	(1<<14)
 
@@ -8116,6 +8119,8 @@ enum {
 #define BXT_DE_PLL_ENABLE		_MMIO(0x46070)
 #define   BXT_DE_PLL_PLL_ENABLE		(1 << 31)
 #define   BXT_DE_PLL_LOCK		(1 << 30)
+#define   CNL_CDCLK_PLL_RATIO(x)	(x)
+#define   CNL_CDCLK_PLL_RATIO_MASK	0xff
 
 /* GEN9 DC */
 #define DC_STATE_EN			_MMIO(0x45504)

drivers/gpu/drm/i915/intel_cdclk.c

@@ -1400,6 +1400,58 @@ void bxt_uninit_cdclk(struct drm_i915_private *dev_priv)
 	bxt_set_cdclk(dev_priv, &cdclk_state);
 }
 
+static void cnl_cdclk_pll_update(struct drm_i915_private *dev_priv,
+				 struct intel_cdclk_state *cdclk_state)
+{
+	u32 val;
+
+	if (I915_READ(SKL_DSSM) & CNL_DSSM_CDCLK_PLL_REFCLK_24MHz)
+		cdclk_state->ref = 24000;
+	else
+		cdclk_state->ref = 19200;
+
+	cdclk_state->vco = 0;
+
+	val = I915_READ(BXT_DE_PLL_ENABLE);
+	if ((val & BXT_DE_PLL_PLL_ENABLE) == 0)
+		return;
+
+	if (WARN_ON((val & BXT_DE_PLL_LOCK) == 0))
+		return;
+
+	cdclk_state->vco = (val & CNL_CDCLK_PLL_RATIO_MASK) * cdclk_state->ref;
+}
+
+static void cnl_get_cdclk(struct drm_i915_private *dev_priv,
+			 struct intel_cdclk_state *cdclk_state)
+{
+	u32 divider;
+	int div;
+
+	cnl_cdclk_pll_update(dev_priv, cdclk_state);
+
+	cdclk_state->cdclk = cdclk_state->ref;
+
+	if (cdclk_state->vco == 0)
+		return;
+
+	divider = I915_READ(CDCLK_CTL) & BXT_CDCLK_CD2X_DIV_SEL_MASK;
+
+	switch (divider) {
+	case BXT_CDCLK_CD2X_DIV_SEL_1:
+		div = 2;
+		break;
+	case BXT_CDCLK_CD2X_DIV_SEL_2:
+		div = 4;
+		break;
+	default:
+		MISSING_CASE(divider);
+		return;
+	}
+
+	cdclk_state->cdclk = DIV_ROUND_CLOSEST(cdclk_state->vco, div);
+}
+
 /**
  * intel_cdclk_state_compare - Determine if two CDCLK states differ
  * @a: first CDCLK state
@@ -1895,7 +1947,9 @@ void intel_init_cdclk_hooks(struct drm_i915_private *dev_priv)
 			skl_modeset_calc_cdclk;
 	}
 
-	if (IS_GEN9_BC(dev_priv))
+	if (IS_CANNONLAKE(dev_priv))
+		dev_priv->display.get_cdclk = cnl_get_cdclk;
+	else if (IS_GEN9_BC(dev_priv))
 		dev_priv->display.get_cdclk = skl_get_cdclk;
 	else if (IS_GEN9_LP(dev_priv))
 		dev_priv->display.get_cdclk = bxt_get_cdclk;