Linux Virtualization - Apr 2019 - [Spice-devel] [PATCH] Revert "drm/qxl: drop prime import/export callbacks"

On Fri, Apr 26, 2019 at 04:21:37PM +0200, Daniel Vetter
wrote:
> On Fri, Apr 26, 2019 at 7:33 AM Gerd Hoffmann <kraxel at redhat.com>
wrote:
> >
> > This reverts commit f4c34b1e2a37d5676180901fa6ff188bcb6371f8.
> >
> > Simliar to commit a0cecc23cfcb Revert "drm/virtio: drop prime
> > import/export callbacks".  We have to do the same with qxl,
> > for the same reasons (it breaks DRI3).
> >
> > Drop the WARN_ON_ONCE().
> >
> > Fixes: f4c34b1e2a37d5676180901fa6ff188bcb6371f8
> > Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> 
> Maybe we need some helpers for virtual drivers which only allow
> self-reimport and nothing else at all?
The current gem prime helpers handle this reasonable well,
I don't see a need for that.

More useful would be some way to signal this self-reimport capability
to userspace somehow.  See DRM_PRIME_CAP_LOCAL patch.

Right now I have the choice to set DRM_PRIME_CAP_{IMPORT,EXPORT}, in
which case some userspace assumes it can do cross-driver export/import
and trips over that not working.  Or I do not set
DRM_PRIME_CAP_{IMPORT,EXPORT}, which breaks DRI3 ...
> I think there's qxl, virgl,
export is implemented for virgl, and import should be possible too.

qxl/bochs is simliar to vmgfx, it could be done but dma-bufs would
basically be bounce buffers (need copy from/to vram) so probably not
worth the effort.

cheers,
  Gerd

On Mon, Apr 29, 2019 at 9:54 AM Gerd Hoffmann <kraxel at redhat.com>
wrote:
>
> On Fri, Apr 26, 2019 at 04:21:37PM +0200, Daniel Vetter wrote:
> > On Fri, Apr 26, 2019 at 7:33 AM Gerd Hoffmann <kraxel at
redhat.com> wrote:
> > >
> > > This reverts commit f4c34b1e2a37d5676180901fa6ff188bcb6371f8.
> > >
> > > Simliar to commit a0cecc23cfcb Revert "drm/virtio: drop
prime
> > > import/export callbacks".  We have to do the same with qxl,
> > > for the same reasons (it breaks DRI3).
> > >
> > > Drop the WARN_ON_ONCE().
> > >
> > > Fixes: f4c34b1e2a37d5676180901fa6ff188bcb6371f8
> > > Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> >
> > Maybe we need some helpers for virtual drivers which only allow
> > self-reimport and nothing else at all?
>
> The current gem prime helpers handle this reasonable well,
> I don't see a need for that.
>
> More useful would be some way to signal this self-reimport capability
> to userspace somehow.  See DRM_PRIME_CAP_LOCAL patch.
Userspace is supposed to test whether import/export works for a
specific combo, not blindly assume it does and then keel over. I think
we need to fix that, not add more flags - there's lots of reasons why
a given pair of devices can't share buffers (e.g. all the contiguous
allocations stuff on socs).
> Right now I have the choice to set DRM_PRIME_CAP_{IMPORT,EXPORT}, in
> which case some userspace assumes it can do cross-driver export/import
> and trips over that not working.  Or I do not set
> DRM_PRIME_CAP_{IMPORT,EXPORT}, which breaks DRI3 ...
Yeah that's not an option.
-Daniel
> > I think there's qxl, virgl,
>
> export is implemented for virgl, and import should be possible too.
>
> qxl/bochs is simliar to vmgfx, it could be done but dma-bufs would
> basically be bounce buffers (need copy from/to vram) so probably not
> worth the effort.
>
> cheers,
>   Gerd
>

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Hi,
> > More useful would be some way to signal this self-reimport capability
> > to userspace somehow.  See DRM_PRIME_CAP_LOCAL patch.
> 
> Userspace is supposed to test whether import/export works for a
> specific combo, not blindly assume it does and then keel over. I think
> we need to fix that, not add more flags - there's lots of reasons why
> a given pair of devices can't share buffers (e.g. all the contiguous
> allocations stuff on socs).
Ok.  Lets scratch the DRM_PRIME_CAP_LOCAL idea then and blame userspace
instead.
> > Right now I have the choice to set DRM_PRIME_CAP_{IMPORT,EXPORT}, in
> > which case some userspace assumes it can do cross-driver export/import
> > and trips over that not working.  Or I do not set
> > DRM_PRIME_CAP_{IMPORT,EXPORT}, which breaks DRI3 ...
> 
> Yeah that's not an option.
Good.  Can I get an ack for this patch then, as it unbreaks DRI3 with qxl?

thanks,
  Gerd