drm/amdgpu: Register ACPI video backlight when skipping amdgpu backlight registration
Typically the acpi_video driver will initialize before amdgpu, which
used to cause /sys/class/backlight/acpi_video0 to get registered and then
amdgpu would register its own amdgpu_bl# 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 amdgpu skips
registering its own backlight device because of either the firmware_flags
or the acpi_video_get_backlight_type() return value. This ensures that
if the acpi_video backlight device should be used, it will be available
before the amdgpu drm_device gets registered with userspace.
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index a64baff..3f45697 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4059,6 +4059,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_display_manager *dm)
if (!acpi_video_backlight_use_native()) {
drm_info(adev_to_drm(dm->adev), "Skipping amdgpu DM backlight registration\n");
+ /* Try registering an ACPI video backlight device instead. */
+ acpi_video_register_backlight();
return;
}
