[PATCH 0/6] Rebase of David Herrmann drm connector link to backlight device

[Daniel Vetter]

On Mon, Oct 24, 2016 at 04:08:47PM +0300, Marta Lofstedt wrote:
> Hi David,
> 
> I am currently investigating:
> https://bugs.freedesktop.org/show_bug.cgi?id=96572
> 
> Martin Peres suggested that your patches:
> https://lists.freedesktop.org/archives/dri-devel/2014-September/thread.html#67984
> could solve the xf86-video-modesetting backlight issues.
> 
> I have rebased your patches and I am working on an IGT
> test for the functionality. With my i915 implementation
> and the small included bug-fix, I can update the drm BACKLIGHT
> property and the value is updated in the backlight class device.
> However, if I set the brigness value through the sysfs file of
> the backlight class device the drm BRIGHTNESS property does not
> update which would be confusing to users.
> 
> My understanding is that DRM properties are cached and, by design,
> do not have the capability to read the status from the driver.
> 
> What do we want to do about this?

Fix it I'd say. But right now there's no callback for drivers to return
non-ATOMIC properties. Only old property values are cached like this. I
guess we can add a get_property hook, which is optional, and which would
fall back to the cached value if need. A bit a pain to wire up, but should
get the job done. Maybe just start out with a callback for connectors
only, instead of all kms objects which can have a property attached.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch