drm/i915: Get proper min cdclk if vDSC enabled

VDSC engine can process only 1 pixel per Cd clock. In case
VDSC is used and max slice count == 1, max supported pixel
clock should be 100% of CD clock. Then do min_cdclk and
pixel clock comparison to get proper min cdclk.

v2:
- Check for dsc enable and slice count ==1 then allow to
  double confirm min cdclk value.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Cooper Chiou <cooper.chiou@intel.com>
Cc: William Tseng <william.tseng@intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210908115607.9633-4-shawn.c.lee@intel.com

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

@@ -2139,6 +2139,16 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
 	/* Account for additional needs from the planes */
 	min_cdclk = max(intel_planes_min_cdclk(crtc_state), min_cdclk);
 
+	/*
+	 * VDSC engine can process only 1 pixel per Cd clock.
+	 * In case VDSC is used and max slice count == 1,
+	 * max supported pixel clock should be 100% of CD clock.
+	 * Then do min_cdclk and pixel clock comparison to get cdclk.
+	 */
+	if (crtc_state->dsc.compression_enable &&
+	    crtc_state->dsc.slice_count == 1)
+		min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate);
+
 	/*
 	 * HACK. Currently for TGL platforms we calculate
 	 * min_cdclk initially based on pixel_rate divided