Re: [PATCH v3] ACPI / video: Add systems that should favor native backlight interface

[Matthew Garrett <matthew.garrett@nebula.com>]

On Tue, 2014-01-21 at 10:24 +0800, Aaron Lu wrote:
> On 01/20/2014 09:34 PM, Matthew Garrett wrote:
> > On Mon, 2014-01-20 at 16:12 +0800, Aaron Lu wrote:
> > 
> >> 1 remove the win8 OSI check, I've seen win7 laptops that also needs to
> >>   have only the GPU interface left and checking win8 doesn't make much
> >>   sense now;
> > 
> > Are we sure that those aren't simply some other bug?
> 
> Well, the firmware on that laptop makes use of EC to do backlight
> control and the fact that the firmware interface doesn't work while the
> GPU's work seems to indicate that the backlight control circuit is not
> routed to EC. I think this is the same case as Win8 laptops.

We know that Windows 8 graphics drivers don't use the ACPI interface,
and that systems change their behaviour as a result, in some cases with
absolutely no way for the ACPI interface could possibly work. I haven't
seen any cases where that's obviously true for any non-Windows 8
systems. EC interfaces that don't work are often due to Linux leaving
the hardware in a state other than the one expected by the firmware. We
shouldn't assume that it's the same issue until we've investigated
further.

-- 
Matthew Garrett <matthew.garrett@nebula.com>