RE: [PATCH 1/6 v8] iommu/fsl: Store iommu domain information pointer in archdata.

-----Original Message-----
From: Alexey Kardashevskiy [mailto:aik@ozlabs.ru]
Sent: Friday, March 01, 2013 4:07 AM
To: Sethi Varun-B16395
Cc: Kumar Gala; Benjamin Herrenschmidt; iommu@lists.linux-foundation.org;=

 linuxppc-dev@lists.ozlabs.org

list; linux-kernel@vger.kernel.org list; Wood Scott-B07421; Yoder Stuart-=

B08248; Joerg Roedel; Paul

Mackerras; David Gibson; Alex Williamson
Subject: Re: [PATCH 1/6 v8] iommu/fsl: Store iommu domain information poi=

nter in archdata.

=20
btw the device struct already has a pointer to its iommu_group, and the
iommu_group struct itself has a pointer void *iommu_data which you could
use for anything you want (iommu_group_get_iommudata(),
iommu_group_set_iommudata()).

By design you are expected to add iommu groups to a domain but not device=

s

so I am not so sure that you really need a pointer to domain in the devic=

e

struct.

Well, at the lowest level the IOMMU API does attach devices to domains-- i.=
e.
API attach_dev().  So, it seems to conceptually make sense to have a ptr
from the device to the associated domain.  When you implement attach_dev()
you need to be able to see whether the device is already attached to
a domain.   Adding a couple of levels of indirection...from device to
group to domain...doesn't seems to make things simpler or better IMHO.

x86 keeps a pointer to the domain in device archdata and since there is
a direct correlation between a device and domain I'd rather see it
where this patch has it.

Stuart