[PATCH v2 13/29] drm/amdgpu: Register ACPI video backlight when skipping amdgpu backlight registration

[Alex Deucher]

On Tue, Jul 12, 2022 at 3:40 PM Hans de Goede <hdegoede at redhat.com> wrote:
>
> 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.
>
> Signed-off-by: Hans de Goede <hdegoede at 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 abf209e36fca..45cd9268b426 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("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;

Can drop the return here.  Either way,
Acked-by: Alex Deucher <alexander.deucher at amd.com>

>  }
>
>  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 3b03a95e59a8..a667e66a9842 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -4054,6 +4054,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_display_manager *dm)
>
>         if (!acpi_video_backlight_use_native()) {
>                 DRM_INFO("Skipping amdgpu DM backlight registration\n");
> +               /* Try registering an ACPI video backlight device instead. */
> +               acpi_video_register_backlight();
>                 return;
>         }
>
> --
> 2.36.0
>