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

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Date:	Fri, 1 Mar 2013 16:21:57 +0000
From:	Yoder Stuart-B08248 <B08248@...escale.com>
To:	Alexey Kardashevskiy <aik@...abs.ru>,
	Sethi Varun-B16395 <B16395@...escale.com>
CC:	Kumar Gala <galak@...nel.crashing.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linuxppc-dev@...ts.ozlabs.org list" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org list" <linux-kernel@...r.kernel.org>,
	Wood Scott-B07421 <B07421@...escale.com>,
	Joerg Roedel <joro@...tes.org>,
	Paul Mackerras <paulus@...ba.org>,
	David Gibson <david@...son.dropbear.id.au>,
	Alex Williamson <alex.williamson@...hat.com>
Subject: RE: [PATCH 1/6 v8] iommu/fsl: Store iommu domain information
 pointer in archdata.



> -----Original Message-----
> From: Alexey Kardashevskiy [mailto:aik@...abs.ru]
> Sent: Friday, March 01, 2013 4:07 AM
> To: Sethi Varun-B16395
> Cc: Kumar Gala; Benjamin Herrenschmidt; iommu@...ts.linux-foundation.org; linuxppc-dev@...ts.ozlabs.org
> list; linux-kernel@...r.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.
> 
> 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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