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

[Simon Ser]

On Friday, June 3rd, 2022 at 16:27, Zack Rusin <zackr at vmware.com> wrote:

> > In particular: since the driver will ignore the KMS cursor plane
> > position set by user-space, I don't think it's okay to just expose
> > without opt-in from user-space (e.g. with a DRM_CLIENT_CAP).
> >
> > cc wayland-devel and Pekka for user-space feedback.
>
> I think Thomas expressed our concerns and reasons why those wouldn’t
> work for us back then. Is there something else you’d like to add?

I disagreed, and I don't understand Thomas' reasoning.

KMS clients will need an update to work correctly. Adding a new prop
without a cap leaves existing KMS clients broken. Adding a cap allows
both existing KMS clients and updated KMS clients to work correctly.

> > On Thursday, June 2nd, 2022 at 17:42, Zack Rusin zack at kde.org wrote:
> >
> > > - all userspace code needs to hardcore a list of drivers which require
> > > hotspots because there's no way to query from drm "does this driver
> > > require hotspot"
> >
> > Can you elaborate? I'm not sure I understand what you mean here.
>
> Only some drivers require informations about cursor hotspot, user space
> currently has no way of figuring out which ones are those, i.e. amdgpu
> doesn’t care about hotspots, qxl does so when running on qxl without
> properly set cursor hotspot atomic kms will result in a desktop where
> mouse clicks have incorrect coordinates.
>
> There’s no way to differentiate between drivers that do not care about
> cursor hotspots and ones that absolutely require it.

Only VM drivers should expose the hotspot properties. Real drivers like
amdgpu must not expose it.