[Intel-gfx] New Samsung driver for backlight control.

[Greg KH]

On Wed, Sep 09, 2009 at 01:04:15PM +0200, Matthias Hopf wrote:
> On Sep 08, 09 09:31:24 -0700, Greg KH wrote:
> > > AFAIR at one point you deliberately decided to expose only 8 levels to
> > > the user - while the hardware was capable of more levels (I think it was
> > > something about some user land tool expecting something like that).
> > > But I may be utterly wrong.
> > 
> > Yes, that was when we were blindly poking in the PCI config space.  We
> > aren't supposed to be doing that :)
> > 
> > > I'd love to have more fine grained control on my NC10 as well.
> > 
> > I have reports that Windows also only supports 8 levels, so that is what
> > this hardware controller is possible of supporting, sorry.
> 
> Hm. This is contradicting. On the one hand the hardware is capable of
> more levels. On the other it isn't *reporting* more levels.
> 
> I wouldn't rely on anything what Windows supports. There can be
> arbitrary limitations in the driver.

The hardware seems to allow multiple levels if you poke a raw value into
a random PCI config location.

However, this is not the correct way to control this hardware, a SMI
call needs to be made instead.  And for that call, only 8 levels are
available.

So it's not a limitation in the Windows driver, it is a limitation in
the BIOS provided by the manufacturer.

thanks,

greg k-h