[Intel-gfx] Legacy backlight control with KMS and BACKLIGHT property

[Matthew Garrett]

On Mon, Aug 17, 2009 at 09:11:26AM -0700, Greg KH wrote:
> On Sun, Aug 16, 2009 at 11:21:16PM +0100, Matthew Garrett wrote:
> > What you probably do want to be doing is checking the mmio backlight 
> > register and seeing whether the chip's in legacy, native or combination 
> > mode.
> 
> How do I do this?

Check the function at the top of i915_opregion.c - the mmio registers 
are documented in volume 3 of the 965 docs, the PCI register is in 
volume 1.

> > The opregion code already does this, so that probably wants to be
> > factored out and another entry point added for systems without any
> > other control method. DMI-strings and hardcoded PCI config writes will
> > work, but it's not really the correct solution.
> 
> As stated before, Samsung said this was the best way to control the
> backlight on these laptops, so should I ignore them?  :)

Basically, yeah. It may be that Samsungs always use the legacy register, 
but there's other hardware that also doesn't have a platform driver or 
ACPI support for this.

-- 
Matthew Garrett | mjg59 at srcf.ucam.org