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

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Arnd Bergmann <arnd@arndb.de>
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>
Subject: Re: [PATCH v1 2/2] dma-mapping-common: add DMA attribute - DMA_ATTR_IOMMU_BYPASS
Date: Tue, 03 Nov 2015 10:08:13 +1100	[thread overview]
Message-ID: <1446505693.17404.20.camel@kernel.crashing.org> (raw)
In-Reply-To: <5270615.Sf6ng964Qt@wuerfel>

On Mon, 2015-11-02 at 22:45 +0100, Arnd Bergmann wrote:
> > 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? ;-)

xHCI for example, vs. something like 10G ethernet... but yes I agree it
sucks. I don't like that sort of policy anywhere in drivers. On the
other hand the platform doesn't have much information to make that sort
of decision either.

Cheers,
Ben.