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

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Date:	Tue, 25 Jun 2013 23:30:37 +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 22:14 +0100, Matthew Garrett wrote:
> On Tue, Jun 25, 2013 at 11:10:11PM +0200, Yves-Alexis Perez wrote:
> > On mar., 2013-06-25 at 21:54 +0100, Matthew Garrett wrote:
> > > I agree, we should standardise the behaviour. And the only way we can 
> > > standardise the behaviour is to leave it up to userspace.
> > > 
> > It's pretty clear we disagree on this and that my opinion won't really
> > matter here. But letting userspace handle that just means broken
> > functionality for those who have the chance (apparently) to have an ACPI
> > backlight interface.
> 
> Which, as we've already established, you don't - Lenovo broke it. Your 
> Thinkpad claims to have 100 available levels, and most of them don't 
> work. The kernel has no way of knowing which levels work and which 
> don't, so leaving this up to the kernel won't actually fix your system 
> either.

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.

Also, if the kernel has no way of knowing which levels work, I fail to
see how userspace can do better.

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?
-- 
Yves-Alexis

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