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

[Yoder Stuart-B08248]

> -----Original Message-----
> From: Alexey Kardashevskiy [mailto:aik@xxxxxxxxx]
> Sent: Friday, March 01, 2013 4:07 AM
> To: Sethi Varun-B16395
> Cc: Kumar Gala; Benjamin Herrenschmidt; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx
> list; linux-kernel@xxxxxxxxxxxxxxx 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.
> 
> 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.

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

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