Re: [PATCH v1 2/2] dma-mapping-common: add DMA attribute - DMA_ATTR_IOMMU_BYPASS

From: David Woodhouse <dwmw2@infradead.org>
To: Shamir Rabinovitch <shamir.rabinovitch@oracle.com>,
	arnd@arndb.de, corbet@lwn.net, linux-doc@vger.kernel.org,
	linux-arch@vger.kernel.org
Cc: Andy Lutomirski <luto@kernel.org>, Joerg Roedel <jroedel@suse.de>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Cornelia Huck <cornelia.huck@de.ibm.com>,
	Sebastian Ott <sebott@linux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	benh@kernel.crashing.org, KVM <kvm@vger.kernel.org>,
	dwmw2@infradead.org, Martin Schwidefsky <schwidefsky@de.ibm.com>,
	linux-s390 <linux-s390@vger.kernel.org>
Subject: Re: [PATCH v1 2/2] dma-mapping-common: add DMA attribute - DMA_ATTR_IOMMU_BYPASS
Date: Wed, 28 Oct 2015 15:30:01 +0900	[thread overview]
Message-ID: <1446013801.3405.183.camel@infradead.org> (raw)
In-Reply-To: <1445789224-28032-2-git-send-email-shamir.rabinovitch@oracle.com>

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On Sun, 2015-10-25 at 09:07 -0700, Shamir Rabinovitch wrote:
> 
> +
> +DMA_ATTR_IOMMU_BYPASS
> +---------------------
> +
> > +For systems with IOMMU it is assumed all DMA translations use the IOMMU.

Not entirely true. We have per-device dma_ops on a most architectures
already, and we were just talking about the need to add them to
POWER/SPARC too, because we need to avoid trying to use the IOMMU to
map virtio devices too.

As we look at that (and make the per-device dma_ops a generic thing
rather than per-arch), we should probably look at folding your case in
too.

-- 
dwmw2

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