linux-kernel - Re: [PATCH] xen: introduce xen_vring_use

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Message-ID: <20200701172219-mutt-send-email-mst@kernel.org>
Date:   Wed, 1 Jul 2020 17:23:32 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>, jgross@...e.com,
        Peng Fan <peng.fan@....com>, x86@...nel.org,
        konrad.wilk@...cle.com, jasowang@...hat.com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, linux-imx@....com,
        xen-devel@...ts.xenproject.org, boris.ostrovsky@...cle.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] xen: introduce xen_vring_use_dma

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

-- 
MST