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: <1392914159.32657.18.camel@kazak.uk.xensource.com>
Date:	Thu, 20 Feb 2014 16:35:59 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Julien Grall <julien.grall@...aro.org>
CC:	<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>
Subject: Re: [PATCH 2/2] arm/xen: Don't use xen DMA ops when the device is
 protected by an IOMMU

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?

Ian.

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