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

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Message-ID: <20180803070638.GB1344@infradead.org>
Date:   Fri, 3 Aug 2018 00:06:38 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@...radead.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 Thu, Aug 02, 2018 at 11:53:08PM +0300, Michael S. Tsirkin wrote:
> > We don't need cache flushing tricks.
> 
> You don't but do real devices on same platform need them?

IBMs power plaforms are always cache coherent.  There are some powerpc
platforms have not cache coherent DMA, but I guess this scheme isn't
intended for them.