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>

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index 9942b05..2004107 100644 (file)
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/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;
+                       }
                }
        }