Re: [PATCH v3 06/11] backlight: Replace fb events with a dedicated function call

[Daniel Thompson <danielt@kernel.org>]

On Thu, Mar 06, 2025 at 03:05:48PM +0100, Thomas Zimmermann wrote:
> Remove support for fb events from backlight subsystem. Provide the
> helper backlight_notify_blank_all() instead. Also export the existing
> helper backlight_notify_blank() to update a single backlight device.
>
> In fbdev, call either helper to inform the backlight subsystem of
> changes to a display's blank state. If the framebuffer device has a
> specific backlight, only update this one; otherwise update all.
>
> v3:
> - declare empty fb_bl_notify_blank() as static inline (kernel test robot)

Looks like there are still configs where we get build failure.


> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

Other than the build issues, generally this looks great. Just a couple
of small issues below.


> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 1c43f579396f..9dc93c5e480b 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -78,11 +77,8 @@ static const char *const backlight_scale_types[] = {
>  	[BACKLIGHT_SCALE_NON_LINEAR]	= "non-linear",
>  };
>
> -#if defined(CONFIG_FB_CORE) || (defined(CONFIG_FB_CORE_MODULE) && \
> -				defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
> -static void backlight_notify_blank(struct backlight_device *bd,
> -				   struct device *display_dev,
> -				   bool fb_on, bool prev_fb_on)
> +void backlight_notify_blank(struct backlight_device *bd, struct device *display_dev,
> +			    bool fb_on, bool prev_fb_on)
>  {
>  	guard(mutex)(&bd->ops_lock);
>
> @@ -103,68 +99,18 @@ static void backlight_notify_blank(struct backlight_device *bd,
>  		}
>  	}
>  }
> +EXPORT_SYMBOL(backlight_notify_blank);

Should this be EXPORT_SYMBOL_GPL()?


>
> -/*
> - * fb_notifier_callback
> - *
> - * This callback gets called when something important happens inside a
> - * framebuffer driver. The backlight core only cares about FB_BLANK_UNBLANK
> - * which is reported to the driver using backlight_update_status()
> - * as a state change.
> - *
> - * There may be several fbdev's connected to the backlight device,
> - * in which case they are kept track of. A state change is only reported
> - * if there is a change in backlight for the specified fbdev.
> - */
> -static int fb_notifier_callback(struct notifier_block *self,
> -				unsigned long event, void *data)
> +void backlight_notify_blank_all(struct device *display_dev, bool fb_on, bool prev_fb_on)
>  {
>  	struct backlight_device *bd;
> -	struct fb_event *evdata = data;
> -	struct fb_info *info = evdata->info;
> -	const int *fb_blank = evdata->data;
> -	struct backlight_device *fb_bd = fb_bl_device(info);
> -	bool fb_on, prev_fb_on;
> -
> -	/* If we aren't interested in this event, skip it immediately ... */
> -	if (event != FB_EVENT_BLANK)
> -		return 0;
> -
> -	bd = container_of(self, struct backlight_device, fb_notif);
> -
> -	if (fb_bd && fb_bd != bd)
> -		return 0;
> -
> -	fb_on = fb_blank[0] == FB_BLANK_UNBLANK;
> -	prev_fb_on = fb_blank[1] == FB_BLANK_UNBLANK;
> -
> -	backlight_notify_blank(bd, info->device, fb_on, prev_fb_on);
> -
> -	return 0;
> -}
> -
> -static int backlight_register_fb(struct backlight_device *bd)
> -{
> -	memset(&bd->fb_notif, 0, sizeof(bd->fb_notif));
> -	bd->fb_notif.notifier_call = fb_notifier_callback;
>
> -	return fb_register_client(&bd->fb_notif);
> -}
> +	guard(mutex)(&backlight_dev_list_mutex);
>
> -static void backlight_unregister_fb(struct backlight_device *bd)
> -{
> -	fb_unregister_client(&bd->fb_notif);
> -}
> -#else
> -static inline int backlight_register_fb(struct backlight_device *bd)
> -{
> -	return 0;
> +	list_for_each_entry(bd, &backlight_dev_list, entry)
> +		backlight_notify_blank(bd, display_dev, fb_on, prev_fb_on);
>  }
> -
> -static inline void backlight_unregister_fb(struct backlight_device *bd)
> -{
> -}
> -#endif /* CONFIG_FB_CORE */
> +EXPORT_SYMBOL(backlight_notify_blank_all);

Same here.


Daniel.