drm/i915/display/dg2: Sanitize CD clock

In case of CD clock squashing the divider is always 1. We don't
need to calculate the divider in use so let's skip that for DG2.

v2: Drop unnecessary local variable (Ville)
v3: Avoid if-else structure (Ville)
[v4: vsyrjala: Fix cd2x divider calculation (Uma),
               Introduce has_cdclk_squasher()]

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211119131348.725220-3-mika.kahola@intel.com

drivers/gpu/drm/i915/display/intel_cdclk.c

@@ -1212,6 +1212,11 @@ static void skl_cdclk_uninit_hw(struct drm_i915_private *dev_priv)
 	skl_set_cdclk(dev_priv, &cdclk_config, INVALID_PIPE);
 }
 
+static bool has_cdclk_squasher(struct drm_i915_private *i915)
+{
+	return IS_DG2(i915);
+}
+
 static const struct intel_cdclk_vals bxt_cdclk_table[] = {
 	{ .refclk = 19200, .cdclk = 144000, .divider = 8, .ratio = 60 },
 	{ .refclk = 19200, .cdclk = 288000, .divider = 4, .ratio = 60 },
@@ -1735,7 +1740,7 @@ static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
 static void bxt_sanitize_cdclk(struct drm_i915_private *dev_priv)
 {
 	u32 cdctl, expected;
-	int cdclk, vco;
+	int cdclk, clock, vco;
 
 	intel_update_cdclk(dev_priv);
 	intel_dump_cdclk_config(&dev_priv->cdclk.hw, "Current CDCLK");
@@ -1771,8 +1776,12 @@ static void bxt_sanitize_cdclk(struct drm_i915_private *dev_priv)
 	expected = skl_cdclk_decimal(cdclk);
 
 	/* Figure out what CD2X divider we should be using for this cdclk */
-	expected |= bxt_cdclk_cd2x_div_sel(dev_priv,
-					   dev_priv->cdclk.hw.cdclk,
+	if (has_cdclk_squasher(dev_priv))
+		clock = dev_priv->cdclk.hw.vco / 2;
+	else
+		clock = dev_priv->cdclk.hw.cdclk;
+
+	expected |= bxt_cdclk_cd2x_div_sel(dev_priv, clock,
 					   dev_priv->cdclk.hw.vco);
 
 	/*