drm/omap: add pin refcounting to omap_framebuffer

omap_framebuffer_pin() and omap_framebuffer_unpin() are currently
broken, as they cannot be called multiple times (i.e. pin, pin, unpin,
unpin), which is what happens in certain cases. This issue causes the
driver to possibly use 0 as an address for a displayed buffer, leading
to OCP error from DSS.

This patch fixes the issue by adding a simple pin_count, used to track
the number of pins.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/omap_fb.c

@@ -86,6 +86,7 @@ struct plane {
 
 struct omap_framebuffer {
 	struct drm_framebuffer base;
+	int pin_count;
 	const struct format *format;
 	struct plane planes[4];
 };
@@ -249,6 +250,11 @@ int omap_framebuffer_pin(struct drm_framebuffer *fb)
 	struct omap_framebuffer *omap_fb = to_omap_framebuffer(fb);
 	int ret, i, n = drm_format_num_planes(fb->pixel_format);
 
+	if (omap_fb->pin_count > 0) {
+		omap_fb->pin_count++;
+		return 0;
+	}
+
 	for (i = 0; i < n; i++) {
 		struct plane *plane = &omap_fb->planes[i];
 		ret = omap_gem_get_paddr(plane->bo, &plane->paddr, true);
@@ -257,6 +263,8 @@ int omap_framebuffer_pin(struct drm_framebuffer *fb)
 		omap_gem_dma_sync(plane->bo, DMA_TO_DEVICE);
 	}
 
+	omap_fb->pin_count++;
+
 	return 0;
 
 fail:
@@ -275,6 +283,11 @@ int omap_framebuffer_unpin(struct drm_framebuffer *fb)
 	struct omap_framebuffer *omap_fb = to_omap_framebuffer(fb);
 	int ret, i, n = drm_format_num_planes(fb->pixel_format);
 
+	omap_fb->pin_count--;
+
+	if (omap_fb->pin_count > 0)
+		return 0;
+
 	for (i = 0; i < n; i++) {
 		struct plane *plane = &omap_fb->planes[i];
 		ret = omap_gem_put_paddr(plane->bo);