[PATCH 2/2] drm/fb: avoid setting 0 depth.

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

If the downscaling fails and we end up with a best_depth of 0,
then ignore it.

This actually works around a cascade of failure, but it the
simplest fix for now.

The scaling patch broke the udl driver, as the udl driver doesn't
expose planes at all, so gets the two default 32-bit formats, but
the udl driver then ask for 16bpp fbdev, and the scaling code falls
over.

This fixes the udl driver since the scaled depth support was added.

Fixes: f4bd542bcaee (drm/fb-helper: Scale back depth to supported maximum)
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Linus Walleij <linus.walleij at linaro.org>
Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 0e9349ff2d16..af2ab640cadb 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1963,7 +1963,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
 				best_depth = fmt->depth;
 		}
 	}
-	if (sizes.surface_depth != best_depth) {
+	if (sizes.surface_depth != best_depth && best_depth) {
 		DRM_INFO("requested bpp %d, scaled depth down to %d",
 			 sizes.surface_bpp, best_depth);
 		sizes.surface_depth = best_depth;
-- 
2.20.1