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

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Date:	Tue, 25 Jun 2013 23:46:01 +0200
From:	Yves-Alexis Perez <corsac@...ian.org>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	linux-acpi@...r.kernel.org, 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, rjw@...k.pl,
	Henrique de Moraes Holschuh <hmh@...ian.org>
Subject: Re: [PATCH 0/3] Fix backlight issues on some Windows 8 systems

On mar., 2013-06-25 at 22:33 +0100, Matthew Garrett wrote:
> > I was referring to “standardize the behaviour by leaving up to
> > userspace”. A lot of thinkpads (for example) (all the pre-windows 8
> > ones) have a perfectly working ACPI backlight interface.
> 
> And this patchset won't alter their behaviour.

Sorry if I was unclear and if my mail implied that. It was about your
remark later in the thread (and the mail from Daniel Vetter)
> 
> > Also, if the kernel has no way of knowing which levels work, I fail to
> > see how userspace can do better.
> 
> It can't. That's why this patchset disables the ACPI interface on 
> Windows 8 systems.
> 
> > I understand that switching to intel_backlight instead of acpi_video0
> > follows what Windows 8 recommends but for me it looks orthogonal to the
> > fact ACPI methods now have some awkward (Lenovo) or broken (Dell). I
> > mean, it's not the first time firmware people break some kernel
> > behavior. I know it's usually not easy to contact them, but shouldn't
> > those methods be fixed, instead of somehow blindly switching to graphic
> > drivers?
> 
> No. The correct answer to all firmware issues is "Are we making the same 
> firmware calls as the version of Windows that this hardware thinks it's 
> running". If Windows 8 doesn't make these calls, we shouldn't make these 
> calls.

But if that introduce regressions, shouldn't workarounds be found then?
Sorry if I keep repeating that but brightness keys handling in-kernel is
quite a useful feature and losing it (because of the “behave exactly
like Windows 8 kernel” policy) is indeed a regression.
-- 
Yves-Alexis

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