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: <alpine.DEB.2.02.1402241214570.4471@kaball.uk.xensource.com>
Date:	Mon, 24 Feb 2014 12:19:11 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Julien Grall <julien.grall@...aro.org>,
	<linux-kernel@...r.kernel.org>, <stefano.stabellini@...citrix.com>,
	<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>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/2] arm/xen: Don't use xen DMA ops when the device is
 protected by an IOMMU

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?
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