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

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Date:   Mon, 5 Nov 2018 19:08:17 +0100
From:   Robert Foss <robert.foss@...labora.com>
To:     Emil Velikov <emil.l.velikov@...il.com>
Cc:     David Airlie <airlied@...ux.ie>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Emil Velikov <emil.velikov@...labora.com>
Subject: Re: [PATCH v4 3/4] drm/virtio: add in/out fence support for explicit
 synchronization

Heya,

On 2018-11-05 18:25, Emil Velikov wrote:
> On Mon, 5 Nov 2018 at 11:42, Robert Foss <robert.foss@...labora.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@...labora.com>
>> Signed-off-by: Robert Foss <robert.foss@...labora.com>
>> Suggested-by: Rob Herring <robh@...nel.org>
>> Reviewed-by: Emil Velikov <emil.velikov@...labora.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.
I can't say I understood that part, but I'll happily spin another revision
with more documentation added.

But the change above does not entirely come from your feedback.
While looking into how other drivers do this, an issue in msm was found.
Since this code is being added to virtgpu now, we might as well do the
right thing here, and also end up with all of the in fence handling in a
single chunk.

> Merging the two patches makes things a bit meh. But as before - it's
> for Gerd to make the final call.
> 
> -Emil
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> dri-devel@...ts.freedesktop.org
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