linux-kernel - Re: [PATCH 1/4] iommu: Add iommu_device_group callback and iommu

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Date:	Thu, 01 Dec 2011 23:14:17 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	David Gibson <dwg@....ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	joerg.roedel@....com, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, chrisw@...hat.com, agraf@...e.de,
	scottwood@...escale.com, B08248@...escale.com
Subject: Re: [PATCH 1/4] iommu: Add iommu_device_group callback and
 iommu_group sysfs entry

On Thu, 2011-12-01 at 07:34 -0700, Alex Williamson wrote:
> > Btw, did we get a quirk for the Ricoh multi-function devices which all
> > need to be in the same group because they do all their DMA from function
> > zero? I think we need another similar quirk for a Marvell SATA
> > controller which seems to do its AHCI DMA from its IDE function; see
> > https://bugzilla.redhat.com/757166
> 
> No, as I mentioned, groups are currently for iommu_ops, not dma_ops,

That doesn't matter. There are multiple devices which do all their DMA
from the same source-id, and which have to be handled together. It
doesn't *matter* that it's a hardware bug in this case, and it's just
because they're multiple PCI devices behind a PCIe bridge in the other
case. The grouping code needs to handle it, whether it's for the benefit
of iommu_ops, dma_ops, or both.

> though it makes sense that iommu drivers could use the group info or
> create common quirk infrastructure for handling broken devices like
> these. 

Well, I think we mostly have a consensus that dma_ops should be
implemented *using* iommu_ops; I'd rather be trying to make things
*consistent* between the two rather than building up the differences.

So I'd definitely go for your "use the group info" option. It is the
*same* info, and needs the *same* quirks.

-- 
dwmw2

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