Re: [PATCH] backlight: add support for disabling backlights via sysfs

[Seth Forshee <seth.forshee@canonical.com>]

On Fri, Jun 29, 2012 at 02:24:38PM +0200, Corentin Chary wrote:
> On Thu, Jun 28, 2012 at 9:36 PM, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> > On Thu, Jun 28, 2012 at 02:30:17PM -0500, Seth Forshee wrote:
> >
> >> I actually don't think Corentin's solution is a bad one. It does suffer
> >> from a couple of shortcomings though. First, it only works for broken
> >> ACPI backlights, and some platforms have other backlight interfaces that
> >> are broken (e.g. the i915 backlight on the MacBook Pro 8,2). Second,
> >> marking backlights as broken in the kernel necessitates ever-expanding
> >> dmi blacklists in some of the platform drivers, unless we can get
> >> vendors to stop providing broken backlight interfaces.
> >
> > Userspace should already be prioritising platform interfaces over raw
> > interfaces, so if gmux works on the Mac then there's no problem.
> 
> Hehe, sometime the platform interface doesn't work and the raw does.
> That's the case on various samsung-laptop since we have absolutely no
> documentation about SABI and no known way to probe if the
> implementation is working or not. But anyway, for samsung-laptop it's
> disabled by default in favor of acpi_video (which is also broken most
> of the time on samsung laptops).

The situation is similar with Toshibas. On some the raw interface is
still the only reliable way to change the backlight. I just got my hands
on one of these models though, so I'm hoping to make some progress on
that front in the near future.