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Message-ID: <20221024131451.lvkesdg3kvyvbi7n@pali>
Date: Mon, 24 Oct 2022 15:14:51 +0200
From: Pali Rohár <pali@...nel.org>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Hans de Goede <hdegoede@...hat.com>,
David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
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"Rafael J. Wysocki" <rafael@...nel.org>,
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Rodrigo Vivi <rodrigo.vivi@...el.com>,
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Subject: Re: [PATCH 00/22] Fallback to native backlight
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).
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