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

Matthew Garrett
2013-06-25T21:33:03Z

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@srcf.ucam.org
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