Laptop Panel brightness control
mjg59 at srcf.ucam.org
Wed Jan 6 11:07:41 PST 2010
On Wed, Jan 06, 2010 at 02:04:48PM -0500, Adam Jackson wrote:
> In the glorious future, when the kernel grows DDC/CI support, we're
> going to end up with a DRM output property for backlight anyway. And we
> definitely want to expose it as RANDR property, because backlight level
> is part of the session state for fast-user-switching.
Even with DDC/CI, it ought to be a backlight device so existing software
works with it...
> But my major problem with exposing it as a backlight class device is the
> same problem I had with trying to use /proc/acpi/video/*/*/edid: The
> kernel doesn't give userspace enough information to know which backlight
> is bound to which output.
This is fixable. We just need to set the parent member to the
appropriate output. The ACPI problem was that we don't have a good way
of binding ACPI outputs to card outputs, which isn't an issue here.
> As with ACPI's EDID method, it's sort of academic, since there's not
> many cases where it's ambiguous. If you've only got one video card,
> then the ACPI EDID methods are yours; if you've only got one
> backlight, then the backlight is yours. But I have no trouble
> imagining (eg) a kiosk machine with two LVDS panels, and, then what.
We just need to populate things appropriately. When the DRM layer is
handling things, there shouldn't be any ambiguity.
Matthew Garrett | mjg59 at srcf.ucam.org
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