Re: [PATCH] Revert "drm/virtio: drop prime import/export callbacks"

From: Emil Velikov <emil.l.velikov@gmail.com>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: oleksandr_andrushchenko@epam.com,
	"ML dri-devel" <dri-devel@lists.freedesktop.org>,
	"Dave Airlie" <airlied@redhat.com>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>
Subject: Re: [PATCH] Revert "drm/virtio: drop prime import/export callbacks"
Date: Tue, 23 Apr 2019 17:17:33 +0100	[thread overview]
Message-ID: <CACvgo52ThtXcbjcgnx5O5=onc3UwedaGs7eWf6z7RPoqo8EuRg@mail.gmail.com> (raw)
In-Reply-To: <20190423140646.2ujxqsjwfuzf4fxp@sirius.home.kraxel.org>

On Tue, 23 Apr 2019 at 15:06, Gerd Hoffmann <kraxel@redhat.com> wrote:
>
> On Tue, Apr 23, 2019 at 12:55:07PM +0100, Emil Velikov wrote:
> > On Tue, 23 Apr 2019 at 09:05, Gerd Hoffmann <kraxel@redhat.com> wrote:
> > >
> > >   Hi,
> > >
> > > > > The DRI3 code extensively uses prime_handle_to_fd and
> > > > > prime_fd_to_handle for self-import.
> > >
> > > The callbacks are not used for self-import.
> > >
> > Userspace converts from it's own handles to a dmabuf fd and vice-versa.
> > I assumed that's called self-import, is it not?
>
> self-import is importing a dma-buf into the driver which created it.
>
> drm_gem_prime.c has a shortcut for that, it'll just increase the gem
> reference count instead of going though a full-blown export/import.
>
> The prime_handle_to_fd and prime_fd_to_handle callbacks are only needed
> for the non-self-import case, where the other driver needs/provides a
> scatter list.
>
Looking at kernel.org and drm-misc-next (as of a couple of hours ago)
there is no drm_gem_prime.c file.
I would imagine you meant drm_prime.c.

Even then, the callbacks "prime_handle_to_fd" and "prime_fd_to_handle"
are used by the ioctls themselves [1] [2].
There is no fall-back when the callbacks are missing - we error out with ENOSYS.

I assume that by "callbacks are only needed" you meant that we should
fix the ioctls to use the callbacks only for the non-self-import case?
If so, that should land first before pulling out the prime callbacks, right?

HTH
Emil

[1] https://cgit.freedesktop.org/drm/drm-misc/tree/drivers/gpu/drm/drm_prime.c?id=9158e3c31163488364c76bf6948507e7640d511f#n870
[2] https://cgit.freedesktop.org/drm/drm-misc/tree/drivers/gpu/drm/drm_prime.c?id=9158e3c31163488364c76bf6948507e7640d511f#n889
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel