drm/i915/display/dg2: Read CD clock from squasher table

To calculate CD clock with squasher unit, we set CD clock ratio to fixed value of 34.
The CD clock value is read from CD clock squasher table.

BSpec: 54034

v2: Read ratio from register (Ville)
    Drop unnecessary local variable (Ville)
    Get CD clock from the given table
v3: Calculate CD clock frequency based on waveform bit pattern (Ville)
[v4: vsyrjala: Actually do a proper blind readout from the hardware]
[v5: vsyrjala: Use 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/20211119131348.725220-5-mika.kahola@intel.com

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

@@ -1466,6 +1466,7 @@ static void bxt_de_pll_readout(struct drm_i915_private *dev_priv,
 static void bxt_get_cdclk(struct drm_i915_private *dev_priv,
 			  struct intel_cdclk_config *cdclk_config)
 {
+	u32 squash_ctl = 0;
 	u32 divider;
 	int div;
 
@@ -1503,7 +1504,21 @@ static void bxt_get_cdclk(struct drm_i915_private *dev_priv,
 		return;
 	}
 
-	cdclk_config->cdclk = DIV_ROUND_CLOSEST(cdclk_config->vco, div);
+	if (has_cdclk_squasher(dev_priv))
+		squash_ctl = intel_de_read(dev_priv, CDCLK_SQUASH_CTL);
+
+	if (squash_ctl & CDCLK_SQUASH_ENABLE) {
+		u16 waveform;
+		int size;
+
+		size = REG_FIELD_GET(CDCLK_SQUASH_WINDOW_SIZE_MASK, squash_ctl) + 1;
+		waveform = REG_FIELD_GET(CDCLK_SQUASH_WAVEFORM_MASK, squash_ctl) >> (16 - size);
+
+		cdclk_config->cdclk = DIV_ROUND_CLOSEST(hweight16(waveform) *
+							cdclk_config->vco, size * div);
+	} else {
+		cdclk_config->cdclk = DIV_ROUND_CLOSEST(cdclk_config->vco, div);
+	}
 
  out:
 	/*