linux-kernel - Re: [PATCH 2/2] arm/xen: Don't use xen DMA ops when the device is protected by an IOMMU

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Message-ID: <20140224151636.GA13489@kroah.com>
Date:	Mon, 24 Feb 2014 07:16:36 -0800
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Ian Campbell <Ian.Campbell@...rix.com>,
	Julien Grall <julien.grall@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	xen-devel@...ts.xenproject.org, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] arm/xen: Don't use xen DMA ops when the device is
 protected by an IOMMU

On Mon, Feb 24, 2014 at 12:19:11PM +0000, Stefano Stabellini wrote:
> CC'ing Greg.
> 
> On Thu, 20 Feb 2014, Ian Campbell wrote:
> > On Thu, 2014-02-20 at 16:21 +0000, Julien Grall wrote:
> > > Only Xen is able to know if a device can safely avoid to use xen-swiotlb.
> > > This patch introduce a new property "protected-devices" for the hypervisor
> > > node which list device which the IOMMU are been correctly programmed by Xen.
> > > 
> > > During Linux boot, Xen specific code will create an hash table which
> > > contains all these devices. The hash table will be used in need_xen_dma_ops
> > > to check if the Xen DMA ops needs to be used for the current device.
> > 
> > Is it out of the question to find a field within struct device itself to
> > store this e.g. in struct device_dma_parameters perhaps and avoid the
> > need for a hashtable lookup.
> > 
> > device->iommu_group might be another option, if we can create our own
> > group?
> 
> I agree that a field in struct device would be ideal.
> Greg, get_maintainer.pl points at you as main maintainer of device.h, do
> you have an opinion on this?

I need a whole lot more context here please.  With a patch would be even
better so that I know exactly what you are referring to...
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