drm/exynos: add wait_for_vblank callback interface.

Changelog v2:
fixed comments.

Changelog v1:
this interface can be used to make sure that hardware overlay is disabled
to avoid that memory region is accessed by dma after gem buffer was released.

Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_drv.h

@@ -37,6 +37,20 @@
 #define MAX_FB_BUFFER	4
 #define DEFAULT_ZPOS	-1
 
+#define _wait_for(COND, MS) ({ \
+	unsigned long timeout__ = jiffies + msecs_to_jiffies(MS);	\
+	int ret__ = 0;							\
+	while (!(COND)) {						\
+		if (time_after(jiffies, timeout__)) {			\
+			ret__ = -ETIMEDOUT;				\
+			break;						\
+		}							\
+	}								\
+	ret__;								\
+})
+
+#define wait_for(COND, MS) _wait_for(COND, MS)
+
 struct drm_device;
 struct exynos_drm_overlay;
 struct drm_connector;
@@ -61,13 +75,16 @@ enum exynos_drm_output_type {
  * @commit: apply hardware specific overlay data to registers.
  * @enable: enable hardware specific overlay.
  * @disable: disable hardware specific overlay.
+ * @wait_for_vblank: wait for vblank interrupt to make sure that
+ *	hardware overlay is disabled.
  */
 struct exynos_drm_overlay_ops {
 	void (*mode_set)(struct device *subdrv_dev,
 			 struct exynos_drm_overlay *overlay);
 	void (*commit)(struct device *subdrv_dev, int zpos);
 	void (*enable)(struct device *subdrv_dev, int zpos);
 	void (*disable)(struct device *subdrv_dev, int zpos);
+	void (*wait_for_vblank)(struct device *subdrv_dev);
 };
 
 /*

drivers/gpu/drm/exynos/exynos_drm_encoder.c

@@ -430,4 +430,14 @@ void exynos_drm_encoder_plane_disable(struct drm_encoder *encoder, void *data)
 
 	if (overlay_ops && overlay_ops->disable)
 		overlay_ops->disable(manager->dev, zpos);
+
+	/*
+	 * wait for vblank interrupt
+	 * - this makes sure that hardware overlay is disabled to avoid
+	 * for the dma accesses to memory after gem buffer was released
+	 * because the setting for disabling the overlay will be updated
+	 * at vsync.
+	 */
+	if (overlay_ops->wait_for_vblank)
+		overlay_ops->wait_for_vblank(manager->dev);
 }