[Intel-gfx] [PATCH v2 12/29] drm/nouveau: Register ACPI video backlight when nv_backlight registration fails

Hans de Goede
2022-07-12T19:40:30Z

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@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
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