drm/i915: Make bxt_set_cdclk() operate in terms of the current vs target DE PLL vco

Make bxt_set_cdclk() more readable by looking at current vs. target
DE PLL vco to determine if the DE PLL needs disabling and/or enabling.
We can also calculate the CD2X divider simply as (vco/cdclk) instead of
depending on magic numbers.

The magic numbers are still needed though, but only to map the supported
cdclk frequencies to corresponding DE PLL frequencies.

Note that w'll now program CDCLK_CTL correctly even for the bypass case.
Actually the CD2X divider should not matter in that case since the
hardware will bypass it too, but the "decimal" part should matter (if we
want to do gmbus/aux with the bypass enabled).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463172100-24715-20-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -5278,6 +5278,30 @@ static int skl_cdclk_decimal(int cdclk)
 	return DIV_ROUND_CLOSEST(cdclk - 1000, 500);
 }
 
+static int bxt_de_pll_vco(struct drm_i915_private *dev_priv, int cdclk)
+{
+	int ratio;
+
+	if (cdclk == dev_priv->cdclk_pll.ref)
+		return 0;
+
+	switch (cdclk) {
+	default:
+		MISSING_CASE(cdclk);
+	case 144000:
+	case 288000:
+	case 384000:
+	case 576000:
+		ratio = 60;
+		break;
+	case 624000:
+		ratio = 65;
+		break;
+	}
+
+	return dev_priv->cdclk_pll.ref * ratio;
+}
+
 static void bxt_de_pll_disable(struct drm_i915_private *dev_priv)
 {
 	I915_WRITE(BXT_DE_PLL_ENABLE, 0);
@@ -5289,13 +5313,14 @@ static void bxt_de_pll_disable(struct drm_i915_private *dev_priv)
 	dev_priv->cdclk_pll.vco = 0;
 }
 
-static void bxt_de_pll_enable(struct drm_i915_private *dev_priv, u32 ratio)
+static void bxt_de_pll_enable(struct drm_i915_private *dev_priv, int vco)
 {
+	int ratio = DIV_ROUND_CLOSEST(vco, dev_priv->cdclk_pll.ref);
 	u32 val;
 
 	val = I915_READ(BXT_DE_PLL_CTL);
 	val &= ~BXT_DE_PLL_RATIO_MASK;
-	val |= ratio;
+	val |= BXT_DE_PLL_RATIO(ratio);
 	I915_WRITE(BXT_DE_PLL_CTL, val);
 
 	I915_WRITE(BXT_DE_PLL_ENABLE, BXT_DE_PLL_PLL_ENABLE);
@@ -5304,54 +5329,42 @@ static void bxt_de_pll_enable(struct drm_i915_private *dev_priv, u32 ratio)
 	if (wait_for((I915_READ(BXT_DE_PLL_ENABLE) & BXT_DE_PLL_LOCK) != 0, 1))
 		DRM_ERROR("timeout waiting for DE PLL lock\n");
 
-	dev_priv->cdclk_pll.vco = ratio * dev_priv->cdclk_pll.ref;
+	dev_priv->cdclk_pll.vco = vco;
 }
 
 static void broxton_set_cdclk(struct drm_i915_private *dev_priv, int cdclk)
 {
-	uint32_t divider;
-	uint32_t ratio;
-	uint32_t current_cdclk;
-	int ret;
+	u32 val, divider;
+	int vco, ret;
 
-	/* frequency = 19.2MHz * ratio / 2 / div{1,1.5,2,4} */
-	switch (cdclk) {
-	case 144000:
+	vco = bxt_de_pll_vco(dev_priv, cdclk);
+
+	DRM_DEBUG_DRIVER("Changing CDCLK to %d kHz (VCO %d kHz)\n", cdclk, vco);
+
+	/* cdclk = vco / 2 / div{1,1.5,2,4} */
+	switch (DIV_ROUND_CLOSEST(vco, cdclk)) {
+	case 8:
 		divider = BXT_CDCLK_CD2X_DIV_SEL_4;
-		ratio = BXT_DE_PLL_RATIO(60);
 		break;
-	case 288000:
+	case 4:
 		divider = BXT_CDCLK_CD2X_DIV_SEL_2;
-		ratio = BXT_DE_PLL_RATIO(60);
 		break;
-	case 384000:
+	case 3:
 		divider = BXT_CDCLK_CD2X_DIV_SEL_1_5;
-		ratio = BXT_DE_PLL_RATIO(60);
 		break;
-	case 576000:
+	case 2:
 		divider = BXT_CDCLK_CD2X_DIV_SEL_1;
-		ratio = BXT_DE_PLL_RATIO(60);
-		break;
-	case 624000:
-		divider = BXT_CDCLK_CD2X_DIV_SEL_1;
-		ratio = BXT_DE_PLL_RATIO(65);
-		break;
-	case 19200:
-		/*
-		 * Bypass frequency with DE PLL disabled. Init ratio, divider
-		 * to suppress GCC warning.
-		 */
-		ratio = 0;
-		divider = 0;
 		break;
 	default:
-		DRM_ERROR("unsupported CDCLK freq %d", cdclk);
+		WARN_ON(cdclk != dev_priv->cdclk_pll.ref);
+		WARN_ON(vco != 0);
 
-		return;
+		divider = BXT_CDCLK_CD2X_DIV_SEL_1;
+		break;
 	}
 
-	mutex_lock(&dev_priv->rps.hw_lock);
 	/* Inform power controller of upcoming frequency change */
+	mutex_lock(&dev_priv->rps.hw_lock);
 	ret = sandybridge_pcode_write(dev_priv, HSW_PCODE_DE_WRITE_FREQ_REQ,
 				      0x80000000);
 	mutex_unlock(&dev_priv->rps.hw_lock);
@@ -5362,40 +5375,26 @@ static void broxton_set_cdclk(struct drm_i915_private *dev_priv, int cdclk)
 		return;
 	}
 
-	current_cdclk = I915_READ(CDCLK_CTL) & CDCLK_FREQ_DECIMAL_MASK;
-	/* convert from .1 fixpoint MHz with -1MHz offset to kHz */
-	current_cdclk = current_cdclk * 500 + 1000;
-
-	/*
-	 * DE PLL has to be disabled when
-	 * - setting to 19.2MHz (bypass, PLL isn't used)
-	 * - before setting to 624MHz (PLL needs toggling)
-	 * - before setting to any frequency from 624MHz (PLL needs toggling)
-	 */
-	if (cdclk == 19200 || cdclk == 624000 ||
-	    current_cdclk == 624000) {
+	if (dev_priv->cdclk_pll.vco != 0 &&
+	    dev_priv->cdclk_pll.vco != vco)
 		bxt_de_pll_disable(dev_priv);
-	}
 
-	if (cdclk != 19200) {
-		uint32_t val;
-
-		bxt_de_pll_enable(dev_priv, ratio);
+	if (dev_priv->cdclk_pll.vco != vco)
+		bxt_de_pll_enable(dev_priv, vco);
 
-		val = divider | skl_cdclk_decimal(cdclk);
-		/*
-		 * FIXME if only the cd2x divider needs changing, it could be done
-		 * without shutting off the pipe (if only one pipe is active).
-		 */
-		val |= BXT_CDCLK_CD2X_PIPE_NONE;
-		/*
-		 * Disable SSA Precharge when CD clock frequency < 500 MHz,
-		 * enable otherwise.
-		 */
-		if (cdclk >= 500000)
-			val |= BXT_CDCLK_SSA_PRECHARGE_ENABLE;
-		I915_WRITE(CDCLK_CTL, val);
-	}
+	val = divider | skl_cdclk_decimal(cdclk);
+	/*
+	 * FIXME if only the cd2x divider needs changing, it could be done
+	 * without shutting off the pipe (if only one pipe is active).
+	 */
+	val |= BXT_CDCLK_CD2X_PIPE_NONE;
+	/*
+	 * Disable SSA Precharge when CD clock frequency < 500 MHz,
+	 * enable otherwise.
+	 */
+	if (cdclk >= 500000)
+		val |= BXT_CDCLK_SSA_PRECHARGE_ENABLE;
+	I915_WRITE(CDCLK_CTL, val);
 
 	mutex_lock(&dev_priv->rps.hw_lock);
 	ret = sandybridge_pcode_write(dev_priv, HSW_PCODE_DE_WRITE_FREQ_REQ,
@@ -5445,8 +5444,7 @@ void broxton_init_cdclk(struct drm_i915_private *dev_priv)
 
 void broxton_uninit_cdclk(struct drm_i915_private *dev_priv)
 {
-	/* Set minimum (bypass) frequency, in effect turning off the DE PLL */
-	broxton_set_cdclk(dev_priv, 19200);
+	broxton_set_cdclk(dev_priv, dev_priv->cdclk_pll.ref);
 }
 
 static int skl_calc_cdclk(int max_pixclk, int vco)