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Re: [Qemu-devel] [PATCH 01/13] driver core: Add iommu_group tracking to

From: Alex Williamson
Subject: Re: [Qemu-devel] [PATCH 01/13] driver core: Add iommu_group tracking to struct device
Date: Fri, 11 May 2012 17:58:01 -0600

On Fri, 2012-05-11 at 16:38 -0700, Greg KH wrote:
> On Fri, May 11, 2012 at 04:55:35PM -0600, Alex Williamson wrote:
> > IOMMU groups allow IOMMU drivers to represent DMA visibility
> > and isolation of devices.  Multiple devices may be grouped
> > together for the purposes of DMA.  Placing a pointer on
> > struct device enable easy access for things like streaming
> > DMA programming and drivers like VFIO.
> > 
> > Signed-off-by: Alex Williamson <address@hidden>
> Can't you get this today from the iommu_ops pointer that is on the bus
> that the device is associated with?  Or can devices on a bus have
> different iommu_group pointers?

The latter, each device on a bus might be it's own group.  This is often
the case on x86 unless PCIe-to-PCI bridges obscure the device
visibility.  Thanks,


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