Re: [PATCH 0/6] drm: Add mouse cursor hotspot support to atomic KMS

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Fri, 10 Jun 2022 10:41:05 +0200
Daniel Vetter <daniel@ffwll.ch> wrote:

> Hi all,
> 
> Kinda top post because the thread is sprawling and I think we need a
> summary/restart. I think there's at least 3 issues here:
> 
> - lack of hotspot property support, which means compositors can't really
>   support hotspot with atomic. Which isn't entirely true, because you
>   totally can use atomic for the primary planes/crtcs and the legacy
>   cursor ioctls, but I understand that people might find that a bit silly :-)
> 
>   Anyway this problme is solved by the patch set here, and I think results
>   in some nice cleanups to boot.
> 
> - the fact that cursors for virtual drivers are not planes, but really
>   special things. Which just breaks the universal plane kms uapi. That
>   part isn't solved, and I do agree with Simon and Pekka that we really
>   should solve this before we unleash even more compositors onto the
>   atomic paths of virtual drivers.
> 
>   I think the simplest solution for this is:
>   1. add a new DRM_PLANE_TYPE_VIRTUAL_CURSOR, and set that for these
>   special cursor planes on all virtual drivers
>   2. add the new "I understand virtual cursors planes" setparam, filter
>   virtual cursor planes for userspace which doesn't set this (like we do
>   right now if userspace doesn't set the universal plane mode)
>   3. backport the above patches to all stable kernels
>   4. make sure the hotspot property is only set on VIRTUAL_CURSOR planes
>   and nothing else in the rebased patch series
> 
> - third issue: These special virtual display properties arent documented.
>   Aside from hotspot there's also suggested X/Y and maybe other stuff. I
>   have no idea what suggested X/Y does and what userspace should do with
>   it. I think we need a new section for virtualized drivers which:
>   - documents all the properties involved
>   - documents the new cap for enabling virtual cursor planes
>   - documents some of the key flows that compositors should implement for
>     best experience
>   - documents how exactly the user experience will degrade if compositors
>     pretend it's just a normal kms driver (maybe put that into each of the
>     special flows that a compositor ideally supports)
>   - whatever other comments and gaps I've missed, I'm sure
>     Simon/Pekka/others will chime in once the patch exists.
> 
> There's a bit of fixing oopsies (virtualized drivers really shouldn't have
> enabled universal planes for their cursors) and debt (all these properties
> predate the push to document stuff so we need to fix that), but I don't
> think it's too much. And I think, from reading the threads, that this
> should cover everything?
> 
> Anything I've missed? Or got completely wrong?

Hi,

sounds like a good plan to me.


Thanks,
pq

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