gpu/drm: ingenic: Avoid null pointer deference in plane atomic update

It is possible that there is no drm_framebuffer associated with a given
plane state.

v2: Handle drm_plane->state which can be NULL too
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20191210144142.33143-2-paul@crapouillou.net
# *** extracted tags ***
Acked-by: Sam Ravnborg <sam@ravnborg.org>

drivers/gpu/drm/ingenic/ingenic-drm.c

@@ -372,14 +372,18 @@ static void ingenic_drm_plane_atomic_update(struct drm_plane *plane,
 	struct ingenic_drm *priv = drm_plane_get_priv(plane);
 	struct drm_plane_state *state = plane->state;
 	unsigned int width, height, cpp;
+	dma_addr_t addr;
 
+	if (state && state->fb) {
+		addr = drm_fb_cma_get_gem_addr(state->fb, state, 0);
 		width = state->crtc->state->adjusted_mode.hdisplay;
 		height = state->crtc->state->adjusted_mode.vdisplay;
 		cpp = state->fb->format->cpp[plane->index];
 
-	priv->dma_hwdesc->addr = drm_fb_cma_get_gem_addr(state->fb, state, 0);
+		priv->dma_hwdesc->addr = addr;
 		priv->dma_hwdesc->cmd = width * height * cpp / 4;
 		priv->dma_hwdesc->cmd |= JZ_LCD_CMD_EOF_IRQ;
+	}
 }
 
 static void ingenic_drm_encoder_atomic_mode_set(struct drm_encoder *encoder,