Bug 84101 - Brightness interface shown in desktop computer with Intel graphics i915
Summary: Brightness interface shown in desktop computer with Intel graphics i915
Alias: None
Product: ACPI
Classification: Unclassified
Component: Power-Video (show other bugs)
Hardware: Intel Linux
: P1 normal
Assignee: Aaron Lu
Depends on:
Reported: 2014-09-08 17:31 UTC by Alicia Boya García
Modified: 2014-10-24 08:18 UTC (History)
2 users (show)

See Also:
Kernel Version: 3.16.1
Regression: No
Bisected commit-id:

`acpidump` output (246.11 KB, text/plain)
2014-09-15 07:59 UTC, Alicia Boya García

Description Alicia Boya García 2014-09-08 17:31:59 UTC
For some reason the kernel detects an `acpi_video0` in /sys/class/backlight even though it is running in a desktop computer whose monitors don't support editing backlight levels on software.

`/sys/class/backlight/acpi_video0/device` is a symlink to the integrated graphic card, listed on `lspci` as the following:

00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor Graphics Controller (rev 09)
Comment 1 Alicia Boya García 2014-09-08 17:43:18 UTC
This is causing GNOME to display brightness controls on my computer which does not support them.

Comment 2 Zhang Rui 2014-09-15 07:56:36 UTC
please attach the acpidump output.
Comment 3 Alicia Boya García 2014-09-15 07:59:39 UTC
Created attachment 150421 [details]
`acpidump` output
Comment 4 Aaron Lu 2014-09-15 08:47:56 UTC
I can think of two ways to solve this problem:
1 Add your system into a DMI table to disable the acpi video interface;
2 Disable acpi video interface for all systems that are desktops, which can be queried from the "PM Profile" field of the FADT table.

I think we can try option 2.
Comment 5 Alicia Boya García 2014-09-15 08:50:00 UTC
Please notice some desktops have brightness interfaces indeed, e.g. HP All in One or iMac computers.
Comment 6 Aaron Lu 2014-09-15 08:53:40 UTC
And that acpi_video interface actually works? If that is the case, we can only do quirk then...
Comment 7 Alicia Boya García 2014-09-15 08:56:47 UTC
For my desktop computer without brightness interface, obviously not. About the all in one computers mentioned above, I don't know.

I faintly recall using once Linux in an iMac, but I don't recall whether brightness controls worked or not.

Anyway, I don't think breaking the brightness interface for such computers is a good idea.
Comment 8 Aaron Lu 2014-10-24 08:18:44 UTC
I don't see a way to solve this problem exposed by firmware, I'll close the bug as will_not_fix.

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