Re: [PATCH 3/5] iommu: Limit iommu_attach/detach_device to devices with their own group

[Thierry Reding]

On Tue, Jan 27, 2015 at 01:08:57AM +0100, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@xxxxxxx>
> 
> This patch changes the behavior of the iommu_attach_device
> and iommu_detach_device functions. With this change these
> functions only work on devices that have their own group.
> For all other devices the iommu_group_attach/detach
> functions must be used.
> 
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> ---
>  drivers/iommu/iommu.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 59 insertions(+), 4 deletions(-)

Sorry for my ignorance, but I don't understand what IOMMU groups are
supposed to be or how to make use of them. It seems like a common idiom
is to simply allocate a new group and add a device to it in the IOMMU's
->add_device() callback, but I fail to see the reason for that.

Can anybody point me to documentation about this? I've looked and I did
not find anything.

Thierry

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