drm/radeon/kms: disable VGA rendering engine before taking over VRAM

Before we use any of VRAM, we need to disable the VGA rendering
engine, this render text mode into a graphical framebuffer
for scanout, however it does this on vblank, and can end up
overwriting the GART table and r600 shader objects.

Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/rv770.c

@@ -229,6 +229,10 @@ static void rv770_mc_resume(struct radeon_device *rdev)
 	WREG32(D1VGA_CONTROL, d1vga_control);
 	WREG32(D2VGA_CONTROL, d2vga_control);
 	WREG32(VGA_RENDER_CONTROL, vga_render_control);
+
+	/* we need to own VRAM, so turn off the VGA renderer here
+	 * to stop it overwriting our objects */
+	radeon_avivo_vga_render_disable(rdev);
 }