drm/fb_cma_helper: Add drm_fb_cma_prepare_fb() helper

Add new drm_fb_cma_prepare_fb() helper function extracted from the
imx-drm driver. This function checks if the plane has DMABUF attached
to it, extracts the exclusive fence from it and attaches it to the
plane state for the atomic helper to wait on it.

Signed-off-by: Marek Vasut <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Lucas Stach <[e-mail]>
Reviewed-by: Lucas Stach <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_fb_cma_helper.c

···
  */
 
 #include <drm/drmP.h>
+#include <drm/drm_atomic.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_crtc_helper.h>
 #include <drm/drm_gem_cma_helper.h>
 #include <drm/drm_fb_cma_helper.h>
+#include <linux/dma-buf.h>
 #include <linux/dma-mapping.h>
 #include <linux/module.h>
+#include <linux/reservation.h>
 
 #define DEFAULT_FBDEFIO_DELAY_MS 50
 
···
 	return fb_cma->obj[plane];
 }
 EXPORT_SYMBOL_GPL(drm_fb_cma_get_gem_obj);
+
+/**
+ * drm_fb_cma_prepare_fb() - Prepare CMA framebuffer
+ * @plane: Which plane
+ * @state: Plane state attach fence to
+ *
+ * This should be put into prepare_fb hook of struct &drm_plane_helper_funcs .
+ *
+ * This function checks if the plane FB has an dma-buf attached, extracts
+ * the exclusive fence and attaches it to plane state for the atomic helper
+ * to wait on.
+ *
+ * There is no need for cleanup_fb for CMA based framebuffer drivers.
+ */
+int drm_fb_cma_prepare_fb(struct drm_plane *plane,
+			  struct drm_plane_state *state)
+{
+	struct dma_buf *dma_buf;
+	struct dma_fence *fence;
+
+	if ((plane->state->fb == state->fb) || !state->fb)
+		return 0;
+
+	dma_buf = drm_fb_cma_get_gem_obj(state->fb, 0)->base.dma_buf;
+	if (dma_buf) {
+		fence = reservation_object_get_excl_rcu(dma_buf->resv);
+		drm_atomic_set_fence_for_plane(state, fence);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(drm_fb_cma_prepare_fb);
 
 #ifdef CONFIG_DEBUG_FS
 static void drm_fb_cma_describe(struct drm_framebuffer *fb, struct seq_file *m)

include/drm/drm_fb_cma_helper.h

···
 struct drm_gem_cma_object *drm_fb_cma_get_gem_obj(struct drm_framebuffer *fb,
 	unsigned int plane);
 
+int drm_fb_cma_prepare_fb(struct drm_plane *plane,
+			  struct drm_plane_state *state);
+
 #ifdef CONFIG_DEBUG_FS
 struct seq_file;