[PATCH weston v5 09/36] cms-colord: find a good head

[Daniel Stone]

Hi,

On 1 February 2018 at 22:00, Derek Foreman <derekf at osg.samsung.com> wrote:
> On 2017-12-14 05:40 AM, Pekka Paalanen wrote:
>> The 'head' member of 'struct weston_output' is going to go unused and
>> then disappear, so stop using it and find a head from the proper list.
>>
>> However, this leaves a problem in cms-colord: if you have multiple
>> monitors driver with the same CRTC, what do you say to the color
>> management system? The monitors could be different, but all the color
>> LUTs etc. are in the CRTC and are shared, as is the framebuffer.
>>
>> Do the simple hack here and just use whatever head happens to be the
>> first in the list.
>
> I am a complete non-expert in this area, so if I'm making no sense feel free
> to tell me to shut up...
>
> I think if someone's going through the effort to properly setup color
> management, then we can't use cloned heads off a single CRTC?
>
> We should probably disallow a CRTCs to drive multiple heads if two or more
> of those heads have differing color profiles?
>
> If I went to the trouble of calibrating two displays, I would probably be
> extremely surprised to see them looking different with clone mode enabled.

Yeah, what Derek said. I think non-homogeneous colour properties when
colour management is enabled, should be cause to unclone. That being
said, it's a niche enough usecase that I'd be comfortable landing it
with documentation that it was a known shortcoming. I'd be super
comfortable landing it if we also had an output configuration tweak we
could use to force non-clone mode, or really even just a simple
out-of-tree patch (or environment variable, a la atomic?) that allows
people to work around it easily enough by disabling clones.

Cheers,
Daniel