linux-kernel - Re: [PATCH 00/22] Fallback to native backlight

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Message-ID: <8ed65e3e-e0b9-05ae-b113-db9d649a1e5a@daynix.com>
Date:   Tue, 25 Oct 2022 12:23:39 +0900
From:   Akihiko Odaki <akihiko.odaki@...nix.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jonathan Corbet <corbet@....net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        "Lee, Chun-Yi" <jlee@...e.com>, Mark Gross <markgross@...nel.org>,
        Corentin Chary <corentin.chary@...il.com>,
        Cezary Jackiewicz <cezary.jackiewicz@...il.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Pali Rohár <pali@...nel.org>,
        Jonathan Woithe <jwoithe@...t42.net>,
        Ike Panhc <ike.pan@...onical.com>,
        Daniel Dadap <ddadap@...dia.com>,
        Kenneth Chan <kenneth.t.chan@...il.com>,
        Mattia Dongili <malattia@...ux.it>,
        Henrique de Moraes Holschuh <hmh@....eng.br>,
        Azael Avalos <coproscefalo@...il.com>,
        Lee Jones <lee@...nel.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Helge Deller <deller@....de>,
        Robert Moore <robert.moore@...el.com>,
        dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org,
        platform-driver-x86@...r.kernel.org,
        acpi4asus-user@...ts.sourceforge.net,
        ibm-acpi-devel@...ts.sourceforge.net, linux-fbdev@...r.kernel.org,
        devel@...ica.org
Subject: Re: [PATCH 00/22] Fallback to native backlight

On 2022/10/25 3:11, Jani Nikula wrote:
> On Tue, 25 Oct 2022, Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>> That aside, the first patch in this series can be applied without the
>> later patches so you may have a look at it. It's fine if you don't merge
>> it though since it does not fix really a pragmatic bug as its message says.
> 
> I think it's problematic because it needlessly ties i915 backlight
> operation to existence of backlight devices that may not be related to
> Intel GPU at all. The direction should be multiple supported backlight
> devices, across GPUs and connectors, but only one per display.
> 
> BR,
> Jani.
> 
> 

Unfortunately it is the current situation (even without this patch), and 
this patch is not meant to fix the particular issue.

This patch replaces the following expression:
acpi_video_get_backlight_type() == acpi_backlight_native

As you can see, acpi_video_get_backlight_type() doesn't take a parameter 
which represents the backlight currently being operated. The problem is 
known and documented in "Brightness handling on devices with multiple 
internal panels" section of Documentation/gpu/todo.rst.

The exiting solution is based on the assumption that no device with i915 
and multiple internal backlights.

Regards,
Akihiko Odaki