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

From: Zack Rusin <zackr@vmware.com>
To: Simon Ser <contact@emersion.fr>
Cc: Martin Krastev <krastevm@vmware.com>,
	David Airlie <airlied@linux.ie>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	Gurchetan Singh <gurchetansingh@chromium.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Pekka Paalanen <ppaalanen@gmail.com>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	wayland-devel <wayland-devel@lists.freedesktop.org>,
	Maaz Mombasawala <mombasawalam@vmware.com>
Subject: Re: [PATCH 0/6] drm: Add mouse cursor hotspot support to atomic KMS
Date: Fri, 3 Jun 2022 14:27:12 +0000	[thread overview]
Message-ID: <0F911D96-1C9B-4EF1-84D7-F5335B3FFEB7@vmware.com> (raw)
In-Reply-To: <wRnf-Lm5zz6v1e-NlnFPteyARuLl-R98mOZZVjePHD5ue7QQNR_TSU7RwYBssgUa7xM5hf7Fe59-gMEj81ESrHY3mu_H7yE0dtGhFHFPTnc=@emersion.fr>

> On Jun 3, 2022, at 10:14 AM, Simon Ser <contact@emersion.fr> wrote:
> 
> Hi,
> 
> Please, read this thread:
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Farchives%2Fdri-devel%2F2020-March%2Fthread.html%23259615&amp;data=05%7C01%7Czackr%40vmware.com%7C05141cb812004e947f0408da456b76e2%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637898625140237028%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=%2BZUG0OFC5SXC8%2Bm3D93AliT0VNJHbc1AEwnhVAnw8WQ%3D&amp;reserved=0
> 
> It has a lot of information about the pitfalls of cursor hotspot and
> other things done by VM software.
> 
> 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?

> On Thursday, June 2nd, 2022 at 17:42, Zack Rusin <zack@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.

z