exynos5420: Clear the framebuffer before making it uncacheable

If we clear the framebuffer and then flush it back to memory using cache
operations, the writes are going to be full cachelines at a time. If we
make it uncacheable first, the writes will be serialized writes of
whatever sized chunks memset uses, probably 4 bytes or less.

Change-Id: I960f87a370e97f9e91236ad796d931573bb3dbb8
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Signed-off-by: Gabe Black <gabeblack@chromium.org>
Reviewed-on: http://review.coreboot.org/3668
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/cpu/samsung/exynos5420/cpu.c

@@ -97,6 +97,8 @@ static void exynos_displayport_init(device_t dev)
 	lcdbase = (uintptr_t)cbmem_add(CBMEM_ID_CONSOLE, fb_size);
 	printk(BIOS_SPEW, "LCD framebuffer base is %p\n", (void *)(lcdbase));
 
+	memset((void *)lcdbase, 0, fb_size);	/* clear the framebuffer */
+
 	/*
 	 * We need to clean and invalidate the framebuffer region and disable
 	 * caching as well. We assume that our dcache <--> memory address
@@ -114,7 +116,6 @@ static void exynos_displayport_init(device_t dev)
 	mmio_resource(dev, 1, lcdbase/KiB, (fb_size + KiB - 1)/KiB);
 	printk(BIOS_DEBUG,
 	       "Initializing Exynos VGA, base %p\n", (void *)lcdbase);
-	memset((void *)lcdbase, 0, fb_size);	/* clear the framebuffer */
 	ret = lcd_ctrl_init(fb_size, &panel, (void *)lcdbase);
 }