From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v1 2/2] dma-mapping-common: add DMA attribute - DMA_ATTR_IOMMU_BYPASS
Date: Mon, 02 Nov 2015 22:45:54 +0100
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Shamir Rabinovitch <shamir.rabinovitch@oracle.com>, David Woodhouse <dwmw2@infradead.org>, Andy Lutomirski <luto@amacapital.net>, Christian Borntraeger <borntraeger@de.ibm.com>, linux-arch <linux-arch@vger.kernel.org>, Paolo Bonzini <pbonzini@redhat.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>, Sebastian Ott <sebott@linux.vnet.ibm.com>, linux-s390 <linux-s390@vger.kernel.org>, Cornelia Huck <cornelia.huck@de.ibm.com>, Joerg Roedel <jroedel@suse.de>, Jonathan Corbet <corbet@lwn.net>, KVM <kvm@vger.kernel.org>, Christoph Hellwig <hch@lst.de>
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On Tuesday 03 November 2015 07:13:28 Benjamin Herrenschmidt wrote:
> On Mon, 2015-11-02 at 14:07 +0200, Shamir Rabinovitch wrote:
> > On Mon, Nov 02, 2015 at 09:00:34PM +1100, Benjamin Herrenschmidt
> > wrote:
> > > 
> > > Chosing on a per-mapping basis *in the back end* might still make
> > > some
> > 
> > In my case, choosing mapping based on the hardware that will use this
> > mappings makes more sense. Most hardware are not that performance 
> > sensitive as the Infiniband hardware.
> 
>  ...
> 
> > The driver know for what hardware it is mapping the memory so it know 
> > if the memory will be used by performance sensitive hardware or not.
> 
> Then I would argue for naming this differently. Make it an optional
> hint "DMA_ATTR_HIGH_PERF" or something like that. Whether this is
> achieved via using a bypass or other means in the backend not the
> business of the driver.
> 

With a name like that, who wouldn't pass that flag? ;-)

	Arnd