linux-kernel - Re: [Update][PATCH 0/3] Fix backlight issues on some Windows 8 systems

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 20 Jul 2013 08:16:56 -0500
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-acpi@...r.kernel.org,
	Matthew Garrett <matthew.garrett@...ula.com>,
	seth.forshee@...onical.com, joeyli.kernel@...il.com,
	daniel.vetter@...ll.ch, intel-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	lenb@...nel.org, Aaron Lu <aaron.lu@...el.com>,
	Igor Gnatenko <i.gnatenko.brain@...il.com>,
	Yves-Alexis Perez <corsac@...ian.org>,
	"Lee, Chun-Yi" <jlee@...e.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>
Subject: Re: [Update][PATCH 0/3] Fix backlight issues on some Windows 8 systems

On Wed, Jul 17, 2013 at 7:16 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Sunday, June 09, 2013 07:01:36 PM Matthew Garrett wrote:
>> Windows 8 introduced new policy for backlight control by pushing it out to
>> graphics drivers. This appears to have coincided with a range of vendors
>> adding Windows 8 checks to their backlight control code which trigger either
>> awkward behaviour (Lenovo) or complete brokenness (some Dells). The simplest
>> thing to do would be to just disable ACPI backlight control entirely if the
>> firmware indicates Windows 8 support, but it's entirely possible that
>> individual graphics drivers might still make use of the ACPI functionality in
>> preference to native control.
>>
>> The first two patches in this series are picked from other patchesets aimed at
>> solving similar problems. The last simply unregisters ACPI backlight control
>> on Windows 8 systems when using an Intel GPU. Similar code could be added to
>> other drivers, but I'm reluctant to do so without further investigation as
>> to the behaviour of the vendor drivers under Windows.
>
> Well, after some more time spent on that, we now have a series of 3 patches
> (different from the $subject one) that we think may be used to address this
> issue.  As far as I can say, it has been tested by multiple people whose
> systems have those problems and they generally saw improvement.
>
> It is not my ideal approach, but it seems to be the least intrusive and/or
> with the least amount of possible side effects that we can do right now
> as a general measure (alternatively, we could create a possibly long
> blacklist table of affected systems with different workarounds for them,
> but let's just say that is not overwhelmingly attractive).
>
> [1/3] Make ACPICA export things that we need for checking OSI(Win8).
>
> [2/3] Make acpi_video_device_find_cap() call acpi_video_init_brightness() even
>       if it is not going to register the backlight interface (needed for
>       Thinkpads).
>
> [3/3] Avoid using ACPI backlight if i915 is in use and the firmware believes
>       we are Windows 8.
>
> Many thanks to everyone involved!

I tried this patch series and it's as I expected, it's the same as
acpi_backlight=vendor, and the intel backlight driver doesn't work
correctly in this machine. If you are actually serious about the
mantra of "no user-space regressions", then for this machine at least,
you need to use the ACPI backlight with Windows8 OSI disabled, until
the intel backlight driver is fixed. My patch does that:

http://article.gmane.org/gmane.linux.acpi.devel/60969

-- 
Felipe Contreras
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/