[PATCH v2 14/29] drm/radeon: Register ACPI video backlight when skipping radeon 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 radeon, which
> used to cause /sys/class/backlight/acpi_video0 to get registered and then
> radeon would register its own radeon_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 radeon skips
> registering its own backlight device because of e.g. 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 radeon drm_device gets registered with userspace.
>
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>

Acked-by: Alex Deucher <alexander.deucher at amd.com>

> ---
>  drivers/gpu/drm/radeon/radeon_encoders.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon_encoders.c b/drivers/gpu/drm/radeon/radeon_encoders.c
> index 46549d5179ee..c1cbebb51be1 100644
> --- a/drivers/gpu/drm/radeon/radeon_encoders.c
> +++ b/drivers/gpu/drm/radeon/radeon_encoders.c
> @@ -30,6 +30,8 @@
>  #include <drm/drm_device.h>
>  #include <drm/radeon_drm.h>
>
> +#include <acpi/video.h>
> +
>  #include "radeon.h"
>  #include "radeon_atombios.h"
>  #include "radeon_legacy_encoders.h"
> @@ -167,7 +169,7 @@ static void radeon_encoder_add_backlight(struct radeon_encoder *radeon_encoder,
>                 return;
>
>         if (radeon_backlight == 0) {
> -               return;
> +               use_bl = false;
>         } else if (radeon_backlight == 1) {
>                 use_bl = true;
>         } else if (radeon_backlight == -1) {
> @@ -193,6 +195,13 @@ static void radeon_encoder_add_backlight(struct radeon_encoder *radeon_encoder,
>                 else
>                         radeon_legacy_backlight_init(radeon_encoder, connector);
>         }
> +
> +       /*
> +        * If there is no native backlight device (which may happen even when
> +        * use_bl==true) try registering an ACPI video backlight device instead.
> +        */
> +       if (!rdev->mode_info.bl_encoder)
> +               acpi_video_register_backlight();
>  }
>
>  void
> --
> 2.36.0
>