linux-kernel - Re: [PATCH 3/5] iommu: Limit iommu_attach/detach

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Date:	Tue, 3 Feb 2015 13:25:07 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	iommu@...ts.linux-foundation.org,
	Will Deacon <will.deacon@....com>,
	Kukjin Kim <kgene@...nel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	Robin Murphy <robin.murphy@....com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	jroedel@...e.de
Subject: Re: [PATCH 3/5] iommu: Limit iommu_attach/detach_device to devices
 with their own group

On Tue, Jan 27, 2015 at 01:08:57AM +0100, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> 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@...e.de>
> ---
>  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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