drm/i915/adl_p: Disable FIFO underrun recovery

The FIFO underrun recovery mechanism has a boatload of cases
where it can't be used. The description is also a bit ambiguous
as it doesn't specify whether plane downscaling needs to be considered
or just pipe downscaling. We may not even have sufficient state
tracking to decide this on demand, so for now just disable the
whole thing.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210526173600.27708-1-ville.syrjala@linux.intel.comReviewed-by: José Roberto de Souza <jose.souza@intel.com>

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

@@ -2209,6 +2209,21 @@ static void icl_set_pipe_chicken(struct intel_crtc *crtc)
 	 * across pipe
 	 */
 	tmp |= PIXEL_ROUNDING_TRUNC_FB_PASSTHRU;
+
+	/*
+	 * "The underrun recovery mechanism should be disabled
+	 *  when the following is enabled for this pipe:
+	 *  WiDi
+	 *  Downscaling (this includes YUV420 fullblend)
+	 *  COG
+	 *  DSC
+	 *  PSR2"
+	 *
+	 * FIXME: enable whenever possible...
+	 */
+	if (IS_ALDERLAKE_P(dev_priv))
+		tmp |= UNDERRUN_RECOVERY_DISABLE;
+
 	intel_de_write(dev_priv, PIPE_CHICKEN(pipe), tmp);
 }
 

drivers/gpu/drm/i915/i915_reg.h

@@ -8362,6 +8362,7 @@ enum {
 #define _PIPEC_CHICKEN				0x72038
 #define PIPE_CHICKEN(pipe)			_MMIO_PIPE(pipe, _PIPEA_CHICKEN,\
 							   _PIPEB_CHICKEN)
+#define   UNDERRUN_RECOVERY_DISABLE		REG_BIT(30)
 #define   PIXEL_ROUNDING_TRUNC_FB_PASSTHRU 	(1 << 15)
 #define   PER_PIXEL_ALPHA_BYPASS_EN		(1 << 7)