linux-kernel - Re: [PATCH 1/2] efi: Save Brightness using EFI on Macs

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Message-ID: <aYiMqKJgtaah8pLW@wunner.de>
Date: Sun, 8 Feb 2026 14:16:24 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Hans de Goede <hansg@...nel.org>
Cc: Atharva Tiwari <atharvatiwarilinuxdev@...il.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH 1/2] efi: Save Brightness using EFI on Macs

On Sun, Feb 08, 2026 at 11:45:55AM +0100, Hans de Goede wrote:
> I was already worried about the shutdown approach on v1,
> but did not say anything since I'm not that familiar
> with apple hw and other apple code is already doing
> something similar.

Yes, macOS saves the brightness so that it's persisted across reboots
and can be set already by the EFI firmware, avoiding a bloom effect
(brightness change) on handover to the OS.  We want to provide the
same seamless user experience on Linux that users have grown accustomed
to on macOS, I think that's a reasonable thing to do.

> But writing a non-volatile EFI variable every 300ms is
> just a very very bad idea.

Agreed.  But what do you think about a delayed write when brightness
is changed, so that brightness is persisted even if the OS crashes?
Users don't change brightness that often, I can't imagine that it
amounts to a significantly higher number of writes than if it's
only done on shutdown.

Thanks,

Lukas