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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Date:	Fri, 14 Mar 2014 23:56:37 +0000
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	Julien Grall <julien.grall@...aro.org>
Cc:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Russell King <linux@....linux.org.uk>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	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>, 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 Fri, Mar 14, 2014 at 04:50:23PM +0000, Julien Grall wrote:
> On 02/24/2014 08:49 PM, Stefano Stabellini wrote:
> > On Mon, 24 Feb 2014, gregkh@...uxfoundation.org wrote: 
> > Julien is proposing to store the list of "safe" devices on an hash table
> > in the Xen specific code (in arch/arm/xen/enlighten.c, see
> > http://marc.info/?l=linux-kernel&m=139291370526082&w=2).
> > Whenever Linux is about to do DMA, we would check in the hashtable to
> > figure out whether we need to go through the swiotlb or we can simply
> > use the native dma_ops.
> > 
> > Ian and I were thinking that it would be much easier and faster to have
> > a "xen_safe_device" parameter in struct device and just check for that.
> > It doesn't actually need to be in struct device, it could simply be a
> > flag in struct device_dma_parameters as Ian was suggesting.
> > 
> > Julien, could you please come up with a simple patch to demonstrate the
> > concept?
> 
> Hello Stefano and Greg,
> 
> Sorry for the late answer. I wrote a simple patch which depend on patch #1.
> Let me know if it's the right direction.

I have no context here, care to start the patch series over?

thanks,

greg k-h
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