Subject: Re: [PATCH] xen: introduce xen_vring_use_dma

Sorry for the late reply -- a couple of conferences kept me busy.


On Wed, 1 Jul 2020, Michael S. Tsirkin wrote:

quoted

On Wed, Jul 01, 2020 at 10:34:53AM -0700, Stefano Stabellini wrote:

quoted

Would you be in favor of a more flexible check along the lines of
the one proposed in the patch that started this thread:

    if (xen_vring_use_dma())
            return true;


xen_vring_use_dma would be implemented so that it returns true when
xen_swiotlb is required and false otherwise.

Just to stress - with a patch like this virtio can *still* use DMA API
if PLATFORM_ACCESS is set. So if DMA API is broken on some platforms
as you seem to be saying, you guys should fix it before doing
something like this..

Yes, DMA API is broken with some interfaces (specifically: rpmesg and trusty),
but for them PLATFORM_ACCESS is never set. That is why the errors weren't
reported before. Xen special case aside, there is no problem under normal
circumstances.


If you are OK with this patch (after a little bit of clean-up), Peng, are you OK
with sending an update or do you want me to?

If you could help, that would be great. You have more expertise in knowing
the whole picture.

Thanks,
Peng.


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