[PATCH v4 3/4] drm/virtio: add in/out fence support for explicit synchronization

[Robert Foss]

Hey Gerd

On 2018-11-12 10:10, Gerd Hoffmann wrote:
> On Fri, Nov 09, 2018 at 06:13:52PM +0100, Robert Foss wrote:
>> Hey Gerd,
>>
>> On 2018-11-09 11:13, Gerd Hoffmann wrote:
>>> On Mon, Nov 05, 2018 at 05:25:05PM +0000, Emil Velikov wrote:
>>>> On Mon, 5 Nov 2018 at 11:42, Robert Foss <robert.foss at collabora.com> wrote:
>>>>>
>>>>> When the execbuf call receives an in-fence it will get the dma_fence
>>>>> related to that fence fd and wait on it before submitting the draw call.
>>>>>
>>>>> On the out-fence side we get fence returned by the submitted draw call
>>>>> and attach it to a sync_file and send the sync_file fd to userspace. On
>>>>> error -1 is returned to userspace.
>>>>>
>>>>> Signed-off-by: Gustavo Padovan <gustavo.padovan at collabora.com>
>>>>> Signed-off-by: Robert Foss <robert.foss at collabora.com>
>>>>> Suggested-by: Rob Herring <robh at kernel.org>
>>>>> Reviewed-by: Emil Velikov <emil.velikov at collabora.com>
>>>>> ---
>>>>>
>>>>> Changes since v3:
>>>>>    - Move all in_fence handling to the same VIRTGPU_EXECBUF_FENCE_FD_IN block
>>>> Fwiw my suggestion was to explicitly document whether the IOCTL can
>>>> support, simultaneously, IN and OUT fence.
>>>
>>> Yes, that would be good.  Code looks like it is supposed to work, but
>>> explicitly saying so in the commit message would be nice.
>>
>> On it! Will send out a v5.
>>
>>>
>>> Also: should we use separate fields for in/out fds?
>>
>> I'm not sure I understand which fields you're referring to.
> 
> fence_in_fd & fence_out_fd in the ioctl struct (patch #2).

I had a look into this and how other drivers are doing it.
msm[1] and etnaviv[2] seem to use the same dual-use variable.

There may be some value to keeping the virtgpu congruent
with the other drivers, but I'll leave the final call up to you.


[1] https://github.com/torvalds/linux/blob/master/include/uapi/drm/msm_drm.h#L223

[2] 
https://github.com/torvalds/linux/blob/master/include/uapi/drm/etnaviv_drm.h#L197

Rob.