Re: [PATCH v4 12/31] drm/nouveau: Register ACPI video backlight when nv_backlight registration fails (v2)

[Lyude Paul <lyude@redhat.com>]

Reviewed-by: Lyude Paul <lyude@redhat.com>

On Wed, 2022-08-24 at 14:15 +0200, Hans de Goede wrote:
> 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.
> 
> Changes in v2:
> - Add nouveau_acpi_video_register_backlight() wrapper to avoid unresolved
>   symbol errors on non X86
> 
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_acpi.c      | 5 +++++
>  drivers/gpu/drm/nouveau/nouveau_acpi.h      | 2 ++
>  drivers/gpu/drm/nouveau/nouveau_backlight.c | 7 +++++++
>  3 files changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> index 1592c9cd7750..8cf096f841a9 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> @@ -391,3 +391,8 @@ bool nouveau_acpi_video_backlight_use_native(void)
>  {
>  	return acpi_video_backlight_use_native();
>  }
> +
> +void nouveau_acpi_video_register_backlight(void)
> +{
> +	acpi_video_register_backlight();
> +}
> diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.h b/drivers/gpu/drm/nouveau/nouveau_acpi.h
> index 3c666c30dfca..e39dd8b94b8b 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_acpi.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_acpi.h
> @@ -12,6 +12,7 @@ void nouveau_unregister_dsm_handler(void);
>  void nouveau_switcheroo_optimus_dsm(void);
>  void *nouveau_acpi_edid(struct drm_device *, struct drm_connector *);
>  bool nouveau_acpi_video_backlight_use_native(void);
> +void nouveau_acpi_video_register_backlight(void);
>  #else
>  static inline bool nouveau_is_optimus(void) { return false; };
>  static inline bool nouveau_is_v1_dsm(void) { return false; };
> @@ -20,6 +21,7 @@ static inline void nouveau_unregister_dsm_handler(void) {}
>  static inline void nouveau_switcheroo_optimus_dsm(void) {}
>  static inline void *nouveau_acpi_edid(struct drm_device *dev, struct drm_connector *connector) { return NULL; }
>  static inline bool nouveau_acpi_video_backlight_use_native(void) { return true; }
> +static inline void nouveau_acpi_video_register_backlight(void) {}
>  #endif
>  
>  #endif
> diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> index d2b8f8c13db4..a614582779ca 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> @@ -436,6 +436,13 @@ 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)
> +		nouveau_acpi_video_register_backlight();
> +
>  	return ret;
>  }
>  

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat