drm: tilcdc: simplify the recovery from sync lost error on rev1

Revision 2 of LCDC suffers from an issue where a SYNC_LOST error
caused by limited memory bandwidth may leave the picture shifted a
couple pixels to the right.

This issue has not been observed on revision 1, while the recovery
mechanism introduces a different issue, where the END_OF_FRAME
interrupt doesn't fire while drm is waiting for vblanks.

On rev1: recover from sync lost errors by simply clearing the
RASTER_ENABLE bit in the RASTER_CTRL register and re-enabling it
again as is suggested by the datasheet.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Jyri Sarha <jsarha@ti.com>

drivers/gpu/drm/tilcdc/tilcdc_crtc.c

@@ -856,7 +856,7 @@ irqreturn_t tilcdc_crtc_irq(struct drm_crtc *crtc)
 	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
 	struct drm_device *dev = crtc->dev;
 	struct tilcdc_drm_private *priv = dev->dev_private;
-	uint32_t stat;
+	uint32_t stat, reg;
 
 	stat = tilcdc_read_irqstatus(dev);
 	tilcdc_clear_irqstatus(dev, stat);
@@ -921,17 +921,26 @@ irqreturn_t tilcdc_crtc_irq(struct drm_crtc *crtc)
 		dev_err_ratelimited(dev->dev, "%s(0x%08x): Sync lost",
 				    __func__, stat);
 		tilcdc_crtc->frame_intact = false;
-		if (tilcdc_crtc->sync_lost_count++ >
-		    SYNC_LOST_COUNT_LIMIT) {
-			dev_err(dev->dev, "%s(0x%08x): Sync lost flood detected, recovering", __func__, stat);
-			queue_work(system_wq, &tilcdc_crtc->recover_work);
-			if (priv->rev == 1)
+		if (priv->rev == 1) {
+			reg = tilcdc_read(dev, LCDC_RASTER_CTRL_REG);
+			if (reg & LCDC_RASTER_ENABLE) {
 				tilcdc_clear(dev, LCDC_RASTER_CTRL_REG,
-					     LCDC_V1_SYNC_LOST_INT_ENA);
-			else
+					     LCDC_RASTER_ENABLE);
+				tilcdc_set(dev, LCDC_RASTER_CTRL_REG,
+					   LCDC_RASTER_ENABLE);
+			}
+		} else {
+			if (tilcdc_crtc->sync_lost_count++ >
+			    SYNC_LOST_COUNT_LIMIT) {
+				dev_err(dev->dev,
+					"%s(0x%08x): Sync lost flood detected, recovering",
+					__func__, stat);
+				queue_work(system_wq,
+					   &tilcdc_crtc->recover_work);
 				tilcdc_write(dev, LCDC_INT_ENABLE_CLR_REG,
 					     LCDC_SYNC_LOST);
-			tilcdc_crtc->sync_lost_count = 0;
+				tilcdc_crtc->sync_lost_count = 0;
+			}
 		}
 	}