Re: [PATCH v3 10/13] xen/iommu: smmu: Check for duplicate stream IDs when registering master devices

[Ian Campbell <ian.campbell@citrix.com>]

On Fri, 2015-01-30 at 18:49 +0000, Julien Grall wrote:
> From: Andreas Herrmann <andreas.herrmann@calxeda.com>
> 
> If DT information lists one stream ID twice for the master devices of
> an SMMU this can cause a multi match when stream ID matching is used.
> For stream ID indexing this might trigger an overwrite of an S2CR that
> is already in use.
> 
> So better check for duplicates when DT information is parsed.
> 
> Taken from the linux ML:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-January/226099.html
> 
> Cc: Andreas Herrmann <herrmann.der.user@googlemail.com>
> Signed-off-by: Andreas Herrmann <andreas.herrmann@calxeda.com>
> Signed-off-by: Julien Grall <julien.grall@linaro.org>

I think you were going to drop this one as it is not strictly required?

I'm still not entirely clear on the motivation for this patch, looking
at the v2 thread I see "But, the developer made have written by mistake
twice the streamid for the device." which I think you were saying that
the DT might, hypothetically, be wrong and have duplicated IDs, is that
right?

Is it a hypothetical problem or have we seen it in a real device-tree?

Ian.