drm/exynos: make sure that hardware overlay for fimd is disabled

Changelog v2:
wait for VSYNC instead of BACKPORCH.

Changelog v1:
the values set to registers will be updated into real registers
at vsync so dma operation could be malfunctioned when accessed
to memory after gem buffer was released. this patch makes sure
that hw overlay is disabled before the gem buffer is 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_fimd.c

@@ -570,10 +570,22 @@ static void fimd_win_disable(struct device *dev, int zpos)
 	win_data->enabled = false;
 }
 
+static void fimd_wait_for_vblank(struct device *dev)
+{
+	struct fimd_context *ctx = get_fimd_context(dev);
+	int ret;
+
+	ret = wait_for((__raw_readl(ctx->regs + VIDCON1) &
+					VIDCON1_VSTATUS_VSYNC), 50);
+	if (ret < 0)
+		DRM_DEBUG_KMS("vblank wait timed out.\n");
+}
+
 static struct exynos_drm_overlay_ops fimd_overlay_ops = {
 	.mode_set = fimd_win_mode_set,
 	.commit = fimd_win_commit,
 	.disable = fimd_win_disable,
+	.wait_for_vblank = fimd_wait_for_vblank,
 };
 
 static struct exynos_drm_manager fimd_manager = {