[PATCH] drm/dp: don't mark the AUX backlight enabled when enabling failed

[Oleg Keri <okerixx@gmail.com>]

If drm_edp_backlight_enable() fails, dp_aux_backlight_update_status()
still marks the backlight as enabled. From then on every brightness
change only updates the level and the enable is never retried, so the
panel stays dark until something blanks and unblanks the backlight.

I hit this after resume on a Samsung ATNA OLED panel, where the first
AUX write can fail while the panel is still waking up.

Return the error instead, so the next update tries to enable again.

Fixes: 10f7b40e4f30 ("drm/panel: add basic DP AUX backlight support")
Signed-off-by: Oleg Keri <okerixx@gmail.com>
---
 drivers/gpu/drm/display/drm_dp_helper.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -4634,7 +4634,9 @@ static int dp_aux_backlight_update_status(struct backlight_device *bd)
 
 	if (!backlight_is_blank(bd)) {
 		if (!bl->enabled) {
-			drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
+			ret = drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
+			if (ret)
+				return ret;
 			bl->enabled = true;
 			return 0;
 		}

base-commit: 4c253ac4b29b8c6cc6fdef8f92d4facde62e63b9
-- 
2.55.0