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Subject: Re: [PATCH 2/5] drm/virtio: add uapi for in and out explicit fences
To:     Emil Velikov <emil.l.velikov@gmail.com>
Cc:     David Airlie <airlied@linux.ie>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
        ML dri-devel <dri-devel@lists.freedesktop.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@lists.linux-foundation.org>,
        Gustavo Padovan <gustavo.padovan@collabora.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Emil Velikov <emil.velikov@collabora.com>
References: <20181025183739.9375-1-robert.foss@collabora.com>
 <20181025183739.9375-3-robert.foss@collabora.com>
 <CACvgo51LU3dAfO-jNcV02ZyYBOv8fKLhG_2QyRrB9XYfGJrzHQ@mail.gmail.com>
 <3a8a03d6-a544-b9f3-15a2-f6a2411bdb28@collabora.com>
 <CACvgo50ARCHZckjxj-eoZbY6U4LA7O4iHQd6X4iQE-xu+Q5hRg@mail.gmail.com>
From:   Robert Foss <robert.foss@collabora.com>
Message-ID: <2a3f25cc-d14c-c0bb-152c-03a6a154df6a@collabora.com>
Date:   Fri, 2 Nov 2018 15:42:34 +0100
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Hey Emil,

On 2018-11-02 14:34, Emil Velikov wrote:
> On Thu, 1 Nov 2018 at 12:56, Robert Foss <robert.foss@collabora.com> wrote:
>> On 2018-10-31 10:38, Emil Velikov wrote:
>>> Hi Rob,
>>>
>>> On Thu, 25 Oct 2018 at 19:38, Robert Foss <robert.foss@collabora.com> wrote:
>>>>
>>>> Add a new field called fence_fd that will be used by userspace to send
>>>> in-fences to the kernel and receive out-fences created by the kernel.
>>>>
>>>> This uapi enables virtio to take advantage of explicit synchronization of
>>>> dma-bufs.
>>>>
>>>> There are two new flags:
>>>>
>>>> * VIRTGPU_EXECBUF_FENCE_FD_IN to be used when passing an in-fence fd.
>>>> * VIRTGPU_EXECBUF_FENCE_FD_OUT to be used when requesting an out-fence fd
>>>>
>>>> The execbuffer IOCTL is now read-write to allow the userspace to read the
>>>> out-fence.
>>>>
>>>> On error -1 should be returned in the fence_fd field.
>>>>
>>>> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
>>>> Signed-off-by: Robert Foss <robert.foss@collabora.com>
>>>> ---
>>>> Changes since v2:
>>>>    - Since exbuf-flags is a new flag, check that unsupported
>>>>      flags aren't set.
>>>>
>>>>    drivers/gpu/drm/virtio/virtgpu_ioctl.c |  5 +++++
>>>>    include/uapi/drm/virtgpu_drm.h         | 13 ++++++++++---
>>>>    2 files changed, 15 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
>>>> index d01a9ed100d1..1af289b28fc4 100644
>>>> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
>>>> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
>>>> @@ -116,9 +116,14 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
>>>>           struct ww_acquire_ctx ticket;
>>>>           void *buf;
>>>>
>>>> +       exbuf->fence_fd = -1;
>>>> +
>>> Move this after the sanity checking.
>>
>> Agreed. Fixed in v4
>>
>>>
>>>>           if (vgdev->has_virgl_3d == false)
>>>>                   return -ENOSYS;
>>>>
>>>> +       if ((exbuf->flags & ~VIRTGPU_EXECBUF_FLAGS))
>>>> +               return -EINVAL;
>>>> +
>>> I assume this did this trigger when using old userspace?
>>
>> No, not as far as I'm aware. This check is there to prevent userspace from
>> polluting the bitspace of flag, so that all free bits can be used for new flags.
>>
>> As far as I understand this is pointed out by a drm driver development document
>> written by danvet, which I unfortunately can't seem to find the link for at the
>> moment.
>>
> Yes that is correct. What I was asking is:
> 
> Does a kernel with this patch, work with mesa lacking the corresponding updates?
> I'd imagine things work just fine.

Yes it does!

> 
> -Emil
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