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.deuc...@amd.com> Signed-off-by: Hans de Goede <hdego...@redhat.com> --- drivers/gpu/drm/amd/amdgpu/atombios_encoders.c | 9 +++++++-- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 ++ 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c index b4e3cedceaf8..6be9ac2b9c5b 100644 --- a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c +++ b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c @@ -184,11 +184,11 @@ void amdgpu_atombios_encoder_init_backlight(struct amdgpu_encoder *amdgpu_encode return; if (!(adev->mode_info.firmware_flags & ATOM_BIOS_INFO_BL_CONTROLLED_BY_GPU)) - return; + goto register_acpi_backlight; if (!acpi_video_backlight_use_native()) { drm_info(dev, "Skipping amdgpu atom DIG backlight registration\n"); - return; + goto register_acpi_backlight; } pdata = kmalloc(sizeof(struct amdgpu_backlight_privdata), GFP_KERNEL); @@ -225,6 +225,11 @@ void amdgpu_atombios_encoder_init_backlight(struct amdgpu_encoder *amdgpu_encode error: kfree(pdata); return; + +register_acpi_backlight: + /* Try registering an ACPI video backlight device instead. */ + acpi_video_register_backlight(); + return; } void 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 66fca99d287e..657b2c0f81c2 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -4033,6 +4033,8 @@ 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; } -- 2.37.2
