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

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Date:   Tue, 13 Dec 2016 07:47:25 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Gustavo Padovan <gustavo@...ovan.org>
Cc:     dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
        David Airlie <airlied@...ux.ie>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/5] drm/virtio: add virtio_gpu_alloc_fence()

  Hi,

> +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;
> +	unsigned long irq_flags;
> +
> +	fence = kmalloc(sizeof(struct virtio_gpu_fence), GFP_ATOMIC);
> +	if (!fence)
> +		return NULL;
> +

> +	spin_lock_irqsave(&drv->lock, irq_flags);
> +	fence->drv = drv;
> +	fence->seq = ++drv->sync_seq;
> +	dma_fence_init(&fence->f, &virtio_fence_ops, &drv->lock,
> +		       drv->context, fence->seq);
> +	spin_unlock_irqrestore(&drv->lock, irq_flags);

seq assignment ...

> +
> +	return fence;
> +}
> +
>  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)
>  {
>  	struct virtio_gpu_fence_driver *drv = &vgdev->fence_drv;
>  	unsigned long irq_flags;
>  
> -	*fence = kmalloc(sizeof(struct virtio_gpu_fence), GFP_ATOMIC);
> -	if ((*fence) == NULL)
> -		return -ENOMEM;
> -
>  	spin_lock_irqsave(&drv->lock, irq_flags);
> -	(*fence)->drv = drv;
> -	(*fence)->seq = ++drv->sync_seq;
> -	dma_fence_init(&(*fence)->f, &virtio_fence_ops, &drv->lock,
> -		       drv->context, (*fence)->seq);

... must stay here.  Otherwise requests can be submitted to the virt
queue with fence sequence numbers out of order.

cheers,
  Gerd