Typically the acpi_video driver will initialize before nouveau, which used to cause /sys/class/backlight/acpi_video0 to get registered and then nouveau would register its own nv_backlight device later. After which the drivers/acpi/video_detect.c code unregistered the acpi_video0 device to avoid there being 2 backlight devices. This means that userspace used to briefly see 2 devices and the disappearing of acpi_video0 after a brief time confuses the systemd backlight level save/restore code, see e.g.: https://bbs.archlinux.org/viewtopic.php?id=269920 To fix this the ACPI video code has been modified to make backlight class device registration a separate step, relying on the drm/kms driver to ask for the acpi_video backlight registration after it is done setting up its native backlight device. Add a call to the new acpi_video_register_backlight() when native backlight device registration has failed / was skipped to ensure that there is a backlight device available before the drm_device gets registered with userspace. Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> --- drivers/gpu/drm/nouveau/nouveau_backlight.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c index 91c504c7b82c..befff2a8b763 100644 --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c @@ -437,6 +437,13 @@ nouveau_backlight_init(struct drm_connector *connector) fail_alloc: kfree(bl); + /* + * If we get here we have an internal panel, but no nv_backlight, + * try registering an ACPI video backlight device instead. + */ + if (ret == 0) + acpi_video_register_backlight(); + return ret; } -- 2.36.0
