drm/udl: Move log-cpp code out of udl_damage_handler()

Computing the cpp value's logarithm in a separate helper function makes
the damage-handler code more readable.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191206085954.9697-6-tzimmermann@suse.de

drivers/gpu/drm/udl/udl_fb.c

@@ -58,6 +58,13 @@ static uint16_t rgb16(uint32_t col)
 }
 #endif
 
+static long udl_log_cpp(unsigned int cpp)
+{
+	if (WARN_ON(!is_power_of_2(cpp)))
+		return -EINVAL;
+	return __ffs(cpp);
+}
+
 static int udl_aligned_damage_clip(struct drm_rect *clip, int x, int y,
 				   int width, int height)
 {
@@ -92,11 +99,6 @@ int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
 	int log_bpp;
 	void *vaddr;
 
-	if (WARN_ON(!is_power_of_2(fb->format->cpp[0])))
-		return -EINVAL;
-
-	log_bpp = __ffs(fb->format->cpp[0]);
-
 	spin_lock(&udl->active_fb_16_lock);
 	if (udl->active_fb_16 != fb) {
 		spin_unlock(&udl->active_fb_16_lock);
@@ -104,6 +106,11 @@ int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
 	}
 	spin_unlock(&udl->active_fb_16_lock);
 
+	ret = udl_log_cpp(fb->format->cpp[0]);
+	if (ret < 0)
+		return ret;
+	log_bpp = ret;
+
 	ret = udl_aligned_damage_clip(&clip, x, y, width, height);
 	if (ret)
 		return ret;