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Subject: Re: [RFC] virtio: support VIRTIO_F_IO_BARRIER
To:     Tiwei Bie <tiwei.bie@intel.com>, mst@redhat.com,
        pbonzini@redhat.com, stefanha@redhat.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Cc:     dan.daly@intel.com, cunming.liang@intel.com, zhihong.wang@intel.com
References: <20180503025955.28816-1-tiwei.bie@intel.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <ab66939d-47fb-5f43-3938-0c156ffc6918@redhat.com>
Date:   Thu, 3 May 2018 15:30:03 +0800
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On 2018年05月03日 10:59, Tiwei Bie wrote:
> This patch introduces the support for VIRTIO_F_IO_BARRIER.
> When this feature is negotiated, driver will use the barriers
> suitable for hardware devices.
>
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> ---
>   drivers/virtio/virtio_ring.c       | 5 +++++
>   include/uapi/linux/virtio_config.h | 8 +++++++-
>   2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 21d464a29cf8..edb565643bf4 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -996,6 +996,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
>   		!context;
>   	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
>   
> +	if (virtio_has_feature(vdev, VIRTIO_F_IO_BARRIER))
> +		vq->weak_barriers = false;
> +
>   	/* No callback?  Tell other side not to bother us. */
>   	if (!callback) {
>   		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> @@ -1164,6 +1167,8 @@ void vring_transport_features(struct virtio_device *vdev)
>   			break;
>   		case VIRTIO_F_IOMMU_PLATFORM:
>   			break;
> +		case VIRTIO_F_IO_BARRIER:
> +			break;
>   		default:
>   			/* We don't understand this bit. */
>   			__virtio_clear_bit(vdev, i);
> diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
> index 308e2096291f..6ca8d24bf468 100644
> --- a/include/uapi/linux/virtio_config.h
> +++ b/include/uapi/linux/virtio_config.h
> @@ -49,7 +49,7 @@
>    * transport being used (eg. virtio_ring), the rest are per-device feature
>    * bits. */
>   #define VIRTIO_TRANSPORT_F_START	28
> -#define VIRTIO_TRANSPORT_F_END		34
> +#define VIRTIO_TRANSPORT_F_END		38
>   
>   #ifndef VIRTIO_CONFIG_NO_LEGACY
>   /* Do we get callbacks when the ring is completely used, even if we've
> @@ -71,4 +71,10 @@
>    * this is for compatibility with legacy systems.
>    */
>   #define VIRTIO_F_IOMMU_PLATFORM		33
> +
> +/*
> + * If clear - driver may use barriers suitable for CPU cores.
> + * If set - driver must use barriers suitable for hardware devices.
> + */
> +#define VIRTIO_F_IO_BARRIER		37
>   #endif /* _UAPI_LINUX_VIRTIO_CONFIG_H */

Hi:

I believe this depends on Michael's patch of

"[PATCH] virtio_ring: switch to dma_XX barriers for rpmsg"

?

Thanks