[PATCH v5 2/2] drm: tilcdc: clear the sync lost bit in crtc isr

[Bartosz Golaszewski]

The frame synchronization error happens when the DMA engine attempts
to read what it believes to be the first word of the video buffer but
it cannot be recognized as such or when the LCDC is starved of data
due to insufficient bandwidth of the system interconnect.

On some SoCs (notably: da850) the memory settings do not meet the
LCDC throughput requirements even after increasing the memory
controller command re-ordering and the LDCD master peripheral
priority, sometimes causing the sync lost error (typically when
changing the resolution).

When the sync lost error occurs, simply reset the input FIFO in the
DMA controller unless a sync lost flood is detected in which case
disable the interrupt.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
---
 drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 50 ++++++++++++++++++++++++++----------
 drivers/gpu/drm/tilcdc/tilcdc_regs.h |  1 +
 2 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index 937697d..c4c6323 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
@@ -163,7 +163,7 @@ static void tilcdc_crtc_enable_irqs(struct drm_device *dev)
 
 	if (priv->rev == 1) {
 		tilcdc_set(dev, LCDC_RASTER_CTRL_REG,
-			LCDC_V1_UNDERFLOW_INT_ENA);
+			LCDC_V1_UNDERFLOW_INT_ENA | LCDC_V1_SYNC_LOST_ENA);
 		tilcdc_set(dev, LCDC_DMA_CTRL_REG,
 			LCDC_V1_END_OF_FRAME_INT_ENA);
 	} else {
@@ -181,7 +181,9 @@ static void tilcdc_crtc_disable_irqs(struct drm_device *dev)
 	/* disable irqs that we might have enabled: */
 	if (priv->rev == 1) {
 		tilcdc_clear(dev, LCDC_RASTER_CTRL_REG,
-			LCDC_V1_UNDERFLOW_INT_ENA | LCDC_V1_PL_INT_ENA);
+			     LCDC_V1_UNDERFLOW_INT_ENA |
+			     LCDC_V1_PL_INT_ENA |
+			     LCDC_V1_SYNC_LOST_ENA);
 		tilcdc_clear(dev, LCDC_DMA_CTRL_REG,
 			LCDC_V1_END_OF_FRAME_INT_ENA);
 	} else {
@@ -885,24 +887,44 @@ irqreturn_t tilcdc_crtc_irq(struct drm_crtc *crtc)
 			wake_up(&tilcdc_crtc->frame_done_wq);
 		}
 
-		if (stat & LCDC_SYNC_LOST) {
-			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, disabling the interrupt", __func__, stat);
-				tilcdc_write(dev, LCDC_INT_ENABLE_CLR_REG,
-					     LCDC_SYNC_LOST);
-			}
-		}
-
 		/* Indicate to LCDC that the interrupt service routine has
 		 * completed, see 13.3.6.1.6 in AM335x TRM.
 		 */
 		tilcdc_write(dev, LCDC_END_OF_INT_IND_REG, 0);
 	}
 
+	if (stat & LCDC_SYNC_LOST) {
+		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, disabling the interrupt",
+				__func__, stat);
+			if (priv->rev == 2)
+				tilcdc_write(dev, LCDC_INT_ENABLE_CLR_REG,
+					     LCDC_SYNC_LOST);
+			else if (priv->rev == 1)
+				tilcdc_clear(dev, LCDC_RASTER_CTRL_REG,
+					     LCDC_V1_SYNC_LOST_ENA);
+		}
+
+		if (priv->rev == 2) {
+			/*
+			 * Indicate to LCDC that the interrupt service routine
+			 * has completed, see 13.3.6.1.6 in AM335x TRM.
+			 */
+			tilcdc_write(dev, LCDC_END_OF_INT_IND_REG, 0);
+		} else if (priv->rev == 1) {
+			/* Reset the input FIFO in the DMA controller. */
+			tilcdc_clear(dev,
+				     LCDC_RASTER_CTRL_REG, LCDC_RASTER_ENABLE);
+			tilcdc_set(dev,
+				   LCDC_RASTER_CTRL_REG, LCDC_RASTER_ENABLE);
+		}
+	}
+
 	return IRQ_HANDLED;
 }
 
diff --git a/drivers/gpu/drm/tilcdc/tilcdc_regs.h b/drivers/gpu/drm/tilcdc/tilcdc_regs.h
index f57c0d6..beb8c21 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_regs.h
+++ b/drivers/gpu/drm/tilcdc/tilcdc_regs.h
@@ -61,6 +61,7 @@
 #define LCDC_V2_UNDERFLOW_INT_ENA                BIT(5)
 #define LCDC_V1_PL_INT_ENA                       BIT(4)
 #define LCDC_V2_PL_INT_ENA                       BIT(6)
+#define LCDC_V1_SYNC_LOST_ENA                    BIT(5)
 #define LCDC_MONOCHROME_MODE                     BIT(1)
 #define LCDC_RASTER_ENABLE                       BIT(0)
 #define LCDC_TFT_ALT_ENABLE                      BIT(23)
-- 
2.9.3