video: add config option to skip framebuffer clear

The use-case is that the thing that loaded u-boot already put a splash
image on screen.  And we want to preserve that until grub boot menu
takes over.

Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/video/Kconfig

@@ -119,6 +119,14 @@ config SYS_WHITE_ON_BLACK
 	 better in low-light situations or to reduce eye strain in some
 	 cases.
 
+config NO_FB_CLEAR
+	bool "Skip framebuffer clear"
+	help
+	  If firmware (whatever loads u-boot) has already put a splash image
+	  on screen, you might want to preserve it until whatever u-boot
+	  loads takes over the screen.  This, for example, can be used to
+	  keep splash image on screen until grub graphical boot menu starts.
+
 source "drivers/video/fonts/Kconfig"
 
 config VIDCONSOLE_AS_LCD

drivers/video/cfb_console.c

@@ -2081,7 +2081,8 @@ static int cfg_video_init(void)
 	}
 	eorx = fgx ^ bgx;
 
-	video_clear();
+	if (!CONFIG_IS_ENABLED(NO_FB_CLEAR))
+		video_clear();
 
 #ifdef CONFIG_VIDEO_LOGO
 	/* Plot the logo and get start point of console */

drivers/video/video-uclass.c

@@ -199,7 +199,9 @@ static int video_post_probe(struct udevice *dev)
 #else
 	priv->colour_bg = 0xffffff;
 #endif
-	video_clear(dev);
+
+	if (!CONFIG_IS_ENABLED(NO_FB_CLEAR))
+		video_clear(dev);
 
 	/*
 	 * Create a text console device. For now we always do this, although