Re: [PATCH vhost v6 08/11] virtio_ring: introduce virtqueue_dma_dev()

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On Tue, Apr 11, 2023 at 1:14 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> On Tue, Apr 11, 2023 at 12:54:46PM +0800, Jason Wang wrote:
> > Ok, just to clarify, I meant there could be a case where the virtqueue
> > is emulated by software, in this case we need check whether the
> > virtqueue has a dma device or not in vring_use_dma_api(). If not we
> > need return false.
> Well, that's what vring_use_dma_api basically does.  Such devics
> just should never have VIRTIO_F_ACCESS_PLATFORM set.  If there is
> a really good reason for such a device to have VIRTIO_F_ACCESS_PLATFORM
> set we'd need an extra quirk in vring_use_dma_api indeed.

This is useful for some vDPA devices where the control virtqueue is
emulated by the vDPA parent (who will decode the control virtqueue
commands to vendor specific control commands).


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