drm/vc4: hvs: Defer updating the enable_bg_fill until vblank

The register to enable/disable background fill was being set
from atomic flush, however that will be applied immediately and
can be a while before the vblank. If it was required for the
current frame but not for the next one, that can result in
corruption for part of the current frame.

Store the state in vc4_hvs, and update it on vblank.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

Author: 6by9

drivers/gpu/drm/vc4/vc4_drv.h

@@ -366,6 +366,8 @@ struct vc4_hvs {
 		unsigned int enabled: 1;
 	} eof_irq[HVS_NUM_CHANNELS];
 
+	bool bg_fill[HVS_NUM_CHANNELS];
+
 	unsigned long max_core_rate;
 
 	/* Memory manager for CRTCs to allocate space in the display

drivers/gpu/drm/vc4/vc4_hvs.c

@@ -1509,14 +1509,7 @@ void vc4_hvs_atomic_flush(struct drm_crtc *crtc,
 		/* This sets a black background color fill, as is the case
 		 * with other DRM drivers.
 		 */
-		if (enable_bg_fill)
-			HVS_WRITE(SCALER6_DISPX_CTRL1(channel),
-				  HVS_READ(SCALER6_DISPX_CTRL1(channel)) |
-				  SCALER6(DISPX_CTRL1_BGENB));
-		else
-			HVS_WRITE(SCALER6_DISPX_CTRL1(channel),
-				  HVS_READ(SCALER6_DISPX_CTRL1(channel)) &
-				  ~SCALER6(DISPX_CTRL1_BGENB));
+		hvs->bg_fill[channel] = enable_bg_fill;
 	} else {
 		/* we can actually run with a lower core clock when background
 		 * fill is enabled on VC4_GEN_5 so leave it enabled always.
@@ -1700,6 +1693,15 @@ static irqreturn_t vc6_hvs_eof_irq_handler(int irq, void *data)
 		if (hvs->eof_irq[i].desc != irq)
 			continue;
 
+		if (hvs->bg_fill[i])
+			HVS_WRITE(SCALER6_DISPX_CTRL1(i),
+				  HVS_READ(SCALER6_DISPX_CTRL1(i)) |
+				  SCALER6(DISPX_CTRL1_BGENB));
+		else
+			HVS_WRITE(SCALER6_DISPX_CTRL1(i),
+				  HVS_READ(SCALER6_DISPX_CTRL1(i)) &
+				  ~SCALER6(DISPX_CTRL1_BGENB));
+
 		vc4_hvs_schedule_dlist_sweep(hvs, i);
 		return IRQ_HANDLED;
 	}