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

[Jesse Barnes]

On Fri, 14 Aug 2009 12:28:47 -0700
Greg KH <greg at kroah.com> wrote:

> On Fri, Aug 14, 2009 at 12:08:21PM -0700, Greg KH wrote:
> > Here's a first cut at such a driver.  It works for me on this
> > laptop, but note that it will try to work on _any_ Intel-based
> > system.  I'll figure out how to do this only for specific machines
> > based on DMI data next.
> 
> And here's one that is set for DMI data to only load on the proper
> ones.
> 
> I'll push this upstream now, if there are no objections.

Yeah, looks fairly reasonable.  This code should work on most pre-965
chipsets too, since they share the LBB regs.  There are a couple of
other things to take into consideration: I think the VBIOS indicates
whether the controls are inverted (i.e. a value of 0xff is minimum
brightness) and there may also be some stepping info.

So ultimately I'd like to see this be part of the i915 driver as one of
a few different methods supported (hopefully we can autodetect them
better than the 2D driver though, using the VBIOS and DMI in the
kernel).

The other three methods that need to export sysfs interfaces are
OpRegion (already done), i2c (some machines have external controllers;
the VBIOS describes how to interact with them) and PWM (the "native"
power modulation regs).

Thanks,
Jesse