Bug#1103397: Missing backlight control on Zhaoxin SoC

From	Ben Hutchings <ben@decadent.org.uk>
Newsgroups	linux.debian.bugs.dist, linux.debian.kernel
Subject	Bug#1103397: Missing backlight control on Zhaoxin SoC
Date	2025-05-14 00:30 +0200
Message-ID	<KM6il-2VJA-1@gated-at.bofh.it> (permalink)
References	(3 earlier) <KKCFH-1VKs-1@gated-at.bofh.it> <KKUVX-27AW-5@gated-at.bofh.it> <KKVoZ-27Lq-3@gated-at.bofh.it> <KET6x-fLik-3@gated-at.bofh.it> <KKVoZ-27Lq-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Sun, 2025-05-11 at 00:28 +0800, Larry Wei wrote:
> P.S. And I suspect that this change has been affecting all non-Intel and 
> non-AMD machines for a long time, as there is no "non-free-firmware" 
> suitable for them.

No, not quite.

By default the ACPI video driver relies on the native graphics driver to
detect which display(s) have a backlight, and to decide whether they
should be controlled via ACPI or via the display controller.

According to <https://linux-hardware.org/?probe=58facb533d> there is no
native driver loaded on your system for the graphics device.  Probably
the EFI framebuffer driver is being used instead.  This has no knowledge
of what kind of display is being used and cannot configure the ACPI
video driver properly.

So the real fix for this would be for Zhaoxin to get their Linux
graphics driver (zx) upstream.  The immediate problem I see with that is
that it's under GPL v3 which is not compatible with the kernel's GPL v2.
But they as copyright holder should be able to relicense it.

Ben.

-- 
Ben Hutchings
Tomorrow will be cancelled due to lack of interest.

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Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane crashes. Larry Wei <larryw3i@yeah.net> - 2025-04-24 10:40 +0200
  Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane crashes. Ben Hutchings <ben@decadent.org.uk> - 2025-04-25 06:00 +0200
  Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-07 21:30 +0200
    Bug#1103397: linux-image-amd64: Kernel Panic:  copy_fpstate_to_sigframe crashes. Salvatore Bonaccorso <carnil@debian.org> - 2025-05-08 22:20 +0200
      Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigframe crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-09 06:00 +0200
        Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigframe crashes. Tony W Wang-oc <TonyWWang-oc@zhaoxin.com> - 2025-05-09 11:10 +0200
          Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigframe crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-09 11:20 +0200
            Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigframe crashes. Tony W Wang-oc <TonyWWang-oc@zhaoxin.com> - 2025-05-09 12:00 +0200
              Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigframe crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-09 15:40 +0200
      Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigframe crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-09 06:10 +0200
    Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane crashes. Ben Hutchings <ben@decadent.org.uk> - 2025-05-09 22:40 +0200
      Processed: Re: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane  crashes. "Debian Bug Tracking System" <owner@bugs.debian.org> - 2025-05-09 22:40 +0200
      Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-10 17:10 +0200
      Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-10 18:10 +0200
        Bug#1103397: linux-image-amd64: Kernel Panic: copy_fpstate_to_sigfrane crashes. Larry Wei <larryw3i@yeah.net> - 2025-05-10 18:40 +0200
          Bug#1103397: Missing backlight control on Zhaoxin SoC Ben Hutchings <ben@decadent.org.uk> - 2025-05-14 00:30 +0200

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