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Date:   Mon, 24 Oct 2022 15:14:51 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Akihiko Odaki <akihiko.odaki@daynix.com>
Cc:     Hans de Goede <hdegoede@redhat.com>,
        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>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        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>,
        Jonathan Woithe <jwoithe@just42.net>,
        Ike Panhc <ike.pan@canonical.com>,
        Daniel Dadap <ddadap@nvidia.com>,
        Kenneth Chan <kenneth.t.chan@gmail.com>,
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        Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        Azael Avalos <coproscefalo@gmail.com>,
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        Daniel Thompson <daniel.thompson@linaro.org>,
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        Helge Deller <deller@gmx.de>,
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        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
Subject: Re: [PATCH 00/22] Fallback to native backlight
Message-ID: <20221024131451.lvkesdg3kvyvbi7n@pali>
References: <20221024113513.5205-1-akihiko.odaki@daynix.com>
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On Monday 24 October 2022 21:58:57 Akihiko Odaki wrote:
> Regarding the second limitation, I don't even understand the difference
> between vendor and native. My guess is that a vendor backlight device uses
> vendor-specific ACPI interface, and a native one directly uses hardware
> registers. If my guess is correct, the difference between vendor and native
> does not imply that both of them are likely to exist at the same time. As
> the conclusion, there is no more motivation to try to de-duplicate the
> vendor/native combination than to try to de-duplicate combination of devices
> with a single type.

Hello! I just want to point one thing. On some Dell laptops there are
3 different ways (= 3 different APIs) how to control display backlight.
There is ACPI driver (uses ACPI), GPU/DRM driver (i915.ko; uses directly
HW) and platform vendor driver (dell-laptop.ko; uses vendor BIOS or
firmware API). Just every driver has different pre-calculated scaling
values. So sometimes user wants to choose different driver just because
it allows to set backlight level with "better" granularity. Registering
all 3 device drivers is bad as user does not want to see 3 display
panels and forcing registration of specific one without runtime option
is also bad (some of those drivers do not have to be suitable or has
worse granularity as other).