On Mon, 14 Aug 2023 11:05:49 +0800, Jason Wang [off-list ref] wrote:

On Thu, Aug 10, 2023 at 8:31 PM Xuan Zhuo [off-list ref] wrote:

quoted

Added virtqueue_dma_dev() to get DMA device for virtio. Then the
caller can do dma operation in advance. The purpose is to keep memory
mapped across multiple add/get buf operations.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>

So I think we don't have actual users for this in this series? Can we
simply have another independent patch for this?

I am ok. I will remove this from the next version.

But I also help merge this to 6.6. Then we can let the virtio-net to support
AF_XDP in 6.7+.

quoted

---
 drivers/virtio/virtio_ring.c | 17 +++++++++++++++++
 include/linux/virtio.h       |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index f9f772e85a38..bb3d73d221cd 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c

@@ -2265,6 +2265,23 @@ int virtqueue_add_inbuf_ctx(struct virtqueue *vq,
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx);

+/**
+ * virtqueue_dma_dev - get the dma dev
+ * @_vq: the struct virtqueue we're talking about.
+ *
+ * Returns the dma dev. That can been used for dma api.
+ */
+struct device *virtqueue_dma_dev(struct virtqueue *_vq)
+{
+       struct vring_virtqueue *vq = to_vvq(_vq);
+
+       if (vq->use_dma_api)
+               return vring_dma_dev(vq);
+       else
+               return NULL;
+}
+EXPORT_SYMBOL_GPL(virtqueue_dma_dev);

One possible concern is that exporting things like NULL may result in
the switch in the caller (driver). I wonder if it's better to do
BUG_ON() in the path of NULL?

I agree.

But we need a new helper to tell the driver(or AF_XDP) that the device support
ACCESS_PLATFORM or not.

We need a switch, but we can make the switch is irrelevant to the DMA.

Thanks.

Thanks

quoted

+
 /**
  * virtqueue_kick_prepare - first half of split virtqueue_kick call.
  * @_vq: the struct virtqueue

diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 8add38038877..bd55a05eec04 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h

@@ -61,6 +61,8 @@ int virtqueue_add_sgs(struct virtqueue *vq,
                      void *data,
                      gfp_t gfp);

+struct device *virtqueue_dma_dev(struct virtqueue *vq);
+
 bool virtqueue_kick(struct virtqueue *vq);

 bool virtqueue_kick_prepare(struct virtqueue *vq);
--

2.32.0.3.g01195cf9f