linux-kernel - Re: [PATCH 1/5] drm/virtio: add virtio_gpu_alloc

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Message-ID: <1c92b6dc-4152-c81b-5180-2f48799b959f@collabora.com>
Date:   Thu, 1 Nov 2018 13:43:51 +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 1/5] drm/virtio: add virtio_gpu_alloc_fence()

Hey Emil,

On 2018-10-31 10:38, Emil Velikov wrote:
> Hi Rob,
> 
> On Thu, 25 Oct 2018 at 19:38, Robert Foss <robert.foss@...labora.com> wrote:
>>
>> From: Gustavo Padovan <gustavo.padovan@...labora.com>
>>
>> Refactor fence creation to remove the potential allocation failure from
>> the cmd_submit and atomic_commit paths. Now the fence should be allocated
>> first and just after we should proceed with the rest of the execution.
>>
> 
> Commit does a bit more that what the above says:
>   - dummy, factor out fence creation/destruction
>   - use per virtio_gpu_framebuffer fence
> 
> Personally I'd keep the two separate patches and elaborate on the latter.
> Obviously in that case, one will need to add 3 lines worth of
> virtio_gpu_fence_alloc() in virtio_gpu_cursor_plane_update which will be nuked
> with the next patch.
> 
> Not a big deal, but it's up-to the maintainer to make the final call if it's
> worth splitting or not.

Agreed, I'll hold off with this change until then.

> 
> Couple of minor nitpicks below.
> 
>>          struct virtio_gpu_device *vgdev = dev->dev_private;
>>          struct virtio_gpu_output *output = NULL;
>>          struct virtio_gpu_framebuffer *vgfb;
>> -       struct virtio_gpu_fence *fence = NULL;
>>          struct virtio_gpu_object *bo = NULL;
>>          uint32_t handle;
>>          int ret = 0;
> 
> Add the virtio_gpu_fence_alloc()? And yes it will be nuked with patch 2/...
> 
> 
> 
>> +struct virtio_gpu_fence *virtio_gpu_fence_alloc(struct virtio_gpu_device *vgdev)
>> +{
>> +       struct virtio_gpu_fence_driver *drv = &vgdev->fence_drv;
>> +       struct virtio_gpu_fence *fence = kzalloc(sizeof(struct virtio_gpu_fence), GFP_ATOMIC);
>> +       if (!fence)
>> +               return fence;
>> +
>> +       fence->drv = drv;
>> +       dma_fence_init(&fence->f, &virtio_fence_ops, &drv->lock, drv->context, 0);
> Oh no, lines over 80 col... while the original code is pretty and neat.

Ack

> 
>> +
>> +       return fence;
>> +}
>> +
>> +void virtio_gpu_fence_cleanup(struct virtio_gpu_fence *fence)
>> +{
>> +       if (!fence)
>> +               return;
>> +
>> +       if (fence->drv)
>> +               dma_fence_put(&fence->f);
>> +       else
>> +               kfree(fence);
> I'm not sure if/how we reach the else case here?

That case should never be hit, and if it is that's a bug.
Fixed in v4.

> 
>> +}
>> +
>>   int virtio_gpu_fence_emit(struct virtio_gpu_device *vgdev,
>>                            struct virtio_gpu_ctrl_hdr *cmd_hdr,
>> -                         struct virtio_gpu_fence **fence)
>> +                         struct virtio_gpu_fence *fence)
>>   {
> 
> With a follow-up commit, we can drop the no longer needed return type.
> Which it turns out was never checked ...
> 

Fixed during drm-misc-next rebase for v4.

> 
> 
>> @@ -319,6 +332,8 @@ static int virtio_gpu_resource_create_ioctl(struct drm_device *dev, void *data,
>>                  dma_fence_put(&fence->f);
>>          }
>>          return 0;
>> +fail_fence:
> 
> The error labels seems to be called after what they do, not what
> fails. fail_backoff seems better IMHO.

Agreed. Fixed in v4.

> 
>> +ttm_eu_backoff_reservation(&ticket, &validate_list);
> Indentation seems off (or my client ate it)?

No, the indentation is bad here. Fixed in v4.

Thanks for the feedback Emil.