linux-kernel - Re: [RFC 0/4] Virtio uses DMA API for all devices

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Date:   Sat, 4 Aug 2018 01:15:00 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Will Deacon <will.deacon@....com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        aik@...abs.ru, robh@...nel.org, joe@...ches.com,
        elfring@...rs.sourceforge.net, david@...son.dropbear.id.au,
        jasowang@...hat.com, mpe@...erman.id.au, linuxram@...ibm.com,
        haren@...ux.vnet.ibm.com, paulus@...ba.org,
        srikar@...ux.vnet.ibm.com, robin.murphy@....com,
        jean-philippe.brucker@....com, marc.zyngier@....com
Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices

On Fri, Aug 03, 2018 at 10:17:32PM +0300, Michael S. Tsirkin wrote:
> It seems reasonable to teach a platform to override dma-range
> for a specific device e.g. in case it knows about bugs in ACPI.

A platform will be able override dma-range using the dev->bus_dma_mask
field starting in 4.19.  But we'll still need a way how to

  a) document in the virtio spec that all bus dma quirks are to be
     applied
  b) a way to document in a virtio-related spec how the bus handles
     dma for Ben's totally fucked up hypervisor.  Without that there
     is not way we'll get interoperable implementations.