If the backlight node is not enabled, this (silently) returns with -EPROBE_DEFER. /sys/kernel/debug/devices_deferred also shows nothing helpful: $ cat /sys/kernel/debug/devices_deferred display

With this patch, there is a helpful hint: $ cat /sys/kernel/debug/devices_deferred display panel-simple: Could not find backlight

Signed-off-by: Alexander Stein alexander.stein@ew.tq-group.com --- drivers/gpu/drm/panel/panel-simple.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c index 4a2e580a2f7b..8fb1c563c96a 100644 --- a/drivers/gpu/drm/panel/panel-simple.c +++ b/drivers/gpu/drm/panel/panel-simple.c @@ -663,8 +663,10 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc) drm_panel_init(&panel->base, dev, &panel_simple_funcs, connector_type);

err = drm_panel_of_backlight(&panel->base); - if (err) + if (err) { + dev_err_probe(dev, err, "Could not find backlight\n"); goto disable_pm_runtime; + }

drm_panel_add(&panel->base);