linux-kernel - Re: [PATCH] backlight: apple_bl: Use acpi_video_get_backlight

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Message-ID: <ZActl7YN+u7Yz58m@smile.fi.intel.com>
Date:   Tue, 7 Mar 2023 14:27:03 +0200
From:   Andy Shevchenko <andy@...nel.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Mark Gross <markgross@...nel.org>, Lee Jones <lee@...nel.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Aditya Garg <gargaditya08@...e.com>,
        platform-driver-x86@...r.kernel.org,
        Matthew Garrett <mjg59@...f.ucam.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: apple_bl: Use acpi_video_get_backlight_type()

On Tue, Mar 07, 2023 at 01:05:40PM +0100, Hans de Goede wrote:
> On some MacBooks both the apple_bl and the apple-gmux backlight drivers
> may be able to export a /sys/class/backlight device.
> 
> To avoid having 2 backlight devices for one LCD panel until now
> the apple-gmux driver has been calling apple_bl_unregister() to move
> the apple_bl backlight device out of the way when it loads.
> 
> Similar problems exist on other x86 laptops and all backlight drivers
> which may be used on x86 laptops have moved to using
> acpi_video_get_backlight_type() to determine whether they should load
> or not.
> 
> Switch apple_bl to this model too, so that it is consistent with all
> the other x86 backlight drivers.
> 
> Besides code-simplification and consistency this has 2 other benefits:
> 
> 1) It removes a race during boot where userspace will briefly see
>    an apple_bl backlight and then have it disappear again, leading to e.g.:
>    https://bbs.archlinux.org/viewtopic.php?id=269920
> 
> 2) This allows user to switch between the drivers by passing
>    acpi_backlight=apple_gmux or acpi_backlight=vendor on the kernel
>    commandline.

...

> +	depends on ACPI_VIDEO=n || ACPI_VIDEO

I'm wondering if "imply ACPI_VIDEO" (i.o.w. weak dependency) is what suitable
here.

-- 
With Best Regards,
Andy Shevchenko