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

[Sethi Varun-B16395]

> -----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@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> linuxppc-dev@xxxxxxxxxxxxxxxx list; linux-kernel@xxxxxxxxxxxxxxx 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.
> 
> 
> 
> > -----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.
> 

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

-Varun

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