linux-kernel - Re: [PATCH v2] iommu/of: Remove PCI host bridge node check

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Message-ID: <49550b7b-b5bc-6687-dc5d-3a71605389ca@arm.com>
Date:   Fri, 22 Sep 2017 10:51:30 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        jean-philippe.brucker@....com
Subject: Re: [PATCH v2] iommu/of: Remove PCI host bridge node check

On 22/09/17 09:56, Joerg Roedel wrote:
> Hey Robin,
> 
> On Thu, Sep 21, 2017 at 11:20:58AM +0100, Robin Murphy wrote:
>> of_pci_iommu_init() tries to be clever and stop its alias walk at the
>> device represented by master_np, in case of weird PCI topologies where
>> the bridge to the IOMMU and the rest of the system is not at the root.
>> It turns out this is a bit short-sighted, since there are plenty of
>> other callers of pci_for_each_dma_alias() which would also need the same
>> behaviour in that situation, and the only platform so far with such a
>> topology (Cavium ThunderX2) already solves it more generally via a PCI
>> quirk. As this check is effectively redundant, and returning a boolean
>> value as an int is a bit broken anyway, let's just get rid of it.
>>
>> Reported-by: Jean-Philippe Brucker <jean-philippe.brucker@....com>
>> Signed-off-by: Robin Murphy <robin.murphy@....com>
> 
> Can you send me a Fixes: tag for this please? No need to resend the
> whole patch, I just need the tag.

Sure, I'd go for:

Fixes: d87beb749281 ("iommu/of: Handle PCI aliases properly")

The check itself originally dates back to b996444cf35e ("iommu/of:
Handle iommu-map property for PCI") but it's really not worth
backporting past the above refactoring - it's only with da4b02750a9f
("iommu/of: Fix of_iommu_configure() for disabled IOMMUs") in 4.14-rc1
that it started to have noticeable ill effects.

Thanks,
Robin.