Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <8ed65e3e-e0b9-05ae-b113-db9d649a1e5a@daynix.com>
Date:   Tue, 25 Oct 2022 12:23:39 +0900
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.3.3
Subject: Re: [PATCH 00/22] Fallback to native backlight
To:     Jani Nikula <jani.nikula@linux.intel.com>,
        Hans de Goede <hdegoede@redhat.com>
Cc:     David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Jonathan Corbet <corbet@lwn.net>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        "Lee, Chun-Yi" <jlee@suse.com>, Mark Gross <markgross@kernel.org>,
        Corentin Chary <corentin.chary@gmail.com>,
        Cezary Jackiewicz <cezary.jackiewicz@gmail.com>,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        =?UTF-8?Q?Pali_Roh=c3=a1r?= <pali@kernel.org>,
        Jonathan Woithe <jwoithe@just42.net>,
        Ike Panhc <ike.pan@canonical.com>,
        Daniel Dadap <ddadap@nvidia.com>,
        Kenneth Chan <kenneth.t.chan@gmail.com>,
        Mattia Dongili <malattia@linux.it>,
        Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        Azael Avalos <coproscefalo@gmail.com>,
        Lee Jones <lee@kernel.org>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        Helge Deller <deller@gmx.de>,
        Robert Moore <robert.moore@intel.com>,
        dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org,
        intel-gfx@lists.freedesktop.org,
        platform-driver-x86@vger.kernel.org,
        acpi4asus-user@lists.sourceforge.net,
        ibm-acpi-devel@lists.sourceforge.net, linux-fbdev@vger.kernel.org,
        devel@acpica.org
References: <20221024113513.5205-1-akihiko.odaki@daynix.com>
 <746e5cc6-516f-8f69-9d4b-8fe237de8fd6@redhat.com>
 <edec5950-cec8-b647-ccb1-ba48f9b3bbb0@daynix.com>
 <60672af8-05d2-113c-12b9-d635608be0dd@redhat.com>
 <ea69242c-0bc8-c7bb-9602-c7489bb69684@daynix.com>
 <7373e258-f7cc-4416-9b1c-c8c9dab59ada@daynix.com>
 <ae3497ed-b68d-c36a-6b6f-f7b9771d9238@redhat.com>
 <78ad5d7b-4078-0b8e-f4aa-6c8113631359@daynix.com> <87o7u1drcz.fsf@intel.com>
Content-Language: en-US
From:   Akihiko Odaki <akihiko.odaki@daynix.com>
In-Reply-To: <87o7u1drcz.fsf@intel.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2022/10/25 3:11, Jani Nikula wrote:
> On Tue, 25 Oct 2022, Akihiko Odaki <akihiko.odaki@daynix.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