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

[Greg KH]

On Sun, Aug 16, 2009 at 02:26:22PM +0100, Matthew Garrett wrote:
> On Fri, Aug 14, 2009 at 12:28:47PM -0700, Greg KH 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.
> 
> This seems basically right, but I don't think DMI's the correct 
> approach. We should be trying the registers on any device that doesn't 
> implement the ACPI code and doesn't provide a more generic 
> platform-specific interface.

How do we know this?  I'll gladly change the driver if there is some
other better way.  Right now I'm only adding laptops that we know need
this kind of configuration as there is no ACPI interface for the
control.

> Speaking of which, are we sure there isn't a Samsung-specific
> interface? Using a platform interface is always preferable to hitting
> the registers directly, since that way we don't have the firmware
> getting out of sync with the hardware.

>From the rumors I have heard from some samsung contacts, they
recommended touching the pci config space directly, which implies that
there is no other way to do this right now :(

thanks,

greg k-h