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

[Keith Packard]

On Fri, 2009-08-14 at 13:45 -0700, Greg KH wrote:

> That's a problem, isn't there some way to figure it out from within the
> kernel?

Not that I know of. Fortunately, we don't have machines with multiple
backlights, at least not many of them.

> But then what about all of the existing drivers already using the
> /sys/class/blacklight interface?

The X server was wrapping this and exposing it as a RandR property, and
so applications could rely on RandR for backlight control for a specific
display. Of course, what we've mostly seen is applications just
using /sys/class/backlight and not caring which monitor it was
affecting.

> Doesn't acpi export this information on lots of machines as well
> already?

Yup, but again, with only one backlight, things are pretty easy.

> The only reason I had to write a new driver for the Samsung hardware,
> was because they were not properly exporting the ACPI tables needed for
> backlight support.  If they had done that, then no one would even be
> having this conversation, which leads me to believe that lots of people
> already depend on the /sys/class/backlight interface today, and that
> will have to be resolved somehow no matter what.

Using either DRM or /sys/class/backlight seems fine to me, aside for the
small problem of associating the /sys/class/backlight with a specific
monitor.

-- 
keith.packard at intel.com
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