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

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Message-ID: <20130625213300.GA3296@srcf.ucam.org>
Date:	Tue, 25 Jun 2013 22:33:00 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Yves-Alexis Perez <corsac@...ian.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 Tue, Jun 25, 2013 at 11:30:37PM +0200, Yves-Alexis Perez wrote:
> On mar., 2013-06-25 at 22:14 +0100, Matthew Garrett wrote:
> > 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.

And this patchset won't alter their behaviour.

> 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.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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