linux-kernel - Re: [PATCH] virtio_pci: use 16-bit accessor for queue

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Message-ID: <20150210065746.GA30095@redhat.com>
Date:	Tue, 10 Feb 2015 07:57:46 +0100
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio_pci: use 16-bit accessor for queue_enable.

On Tue, Feb 10, 2015 at 05:05:01PM +1030, Rusty Russell wrote:
> Since PCI is little endian, 8-bit access might work, but the spec section
> is very clear on this:
> 
>   4.1.3.1 Driver Requirements: PCI Device Layout
> 
>   The driver MUST access each field using the “natural” access method,
>   i.e. 32-bit accesses for 32-bit fields, 16-bit accesses for 16-bit
>   fields and 8-bit accesses for 8-bit fields.
> 
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> index f16e462cb4ef..2aa38e59db2e 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -294,7 +294,7 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
>  
>  	/* Check if queue is either not available or already active. */
>  	num = ioread16(&cfg->queue_size);
> -	if (!num || ioread8(&cfg->queue_enable))
> +	if (!num || ioread16(&cfg->queue_enable))
>  		return ERR_PTR(-ENOENT);
>  
>  	if (num & (num - 1)) {
> @@ -394,7 +394,7 @@ static int vp_modern_find_vqs(struct virtio_device *vdev, unsigned nvqs,
>  	 */
>  	list_for_each_entry(vq, &vdev->vqs, list) {
>  		iowrite16(vq->index, &vp_dev->common->queue_select);
> -		iowrite8(1, &vp_dev->common->queue_enable);
> +		iowrite16(1, &vp_dev->common->queue_enable);
>  	}
>  
>  	return 0;
--
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