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

-----Original Message-----
From: Yoder Stuart-B08248
Sent: Friday, March 01, 2013 9:52 PM
To: Alexey Kardashevskiy; 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; Joerg Roedel; Paul Mackerras; David Gibson; Alex
Williamson
Subject: RE: [PATCH 1/6 v8] iommu/fsl: Store iommu domain information
pointer in archdata.
=20
=20
=20

quoted

-----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

pointer in archdata.

quoted

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
devices so I am not so sure that you really need a pointer to domain
in the device struct.

=20
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.
=20
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.
=20

As Stuart stated this allows us to maintain the device <-> domain relations=
hip at the lowest level.

-Varun