Re: [Xen-devel] [PATCH v2 10/12] xen/iommu: smmu: Check for duplicate stream IDs when registering master devices

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2015-01-27 at 17:33 +0000, Julien Grall wrote:
> On 27/01/15 17:02, Stefano Stabellini wrote:
> > On Tue, 27 Jan 2015, Julien Grall wrote:
> >> On 27/01/15 16:30, Stefano Stabellini wrote:
> >>> On Fri, 16 Jan 2015, Julien Grall wrote:
> >>>> From: Andreas Herrmann <andreas.herrmann@xxxxxxxxxxx>
> >>>>
> >>>> 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@xxxxxxxxxxxxxx>
> >>>> Signed-off-by: Andreas Herrmann <andreas.herrmann@xxxxxxxxxxx>
> >>>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> >>>
> >>> Why didn't you just take a more recent version of the Linux smmu driver?
> >>
> >> The SMMU driver very is recent (see commit in the previous patch)...
> >> Just this patch has never reached upstream.
> > 
> > That is not good. It might be worth to wait for it to go upstream.
> 
> The patch was sent one year ago. Just before Calxeda was shutdown.
> 
> This is a requirement for the following patch. Do you think the other
> patch should be upstream to Linux before?

In general we should be reluctant to diverge over these things, since it
just ends up making things harder for us in the future (e.g. the next
resync or the one after).

Is the issue being fixed here specific to Calxeda? e.g. is duplicate
stream ids a h/w bug which has yet to be observed elsewhere or is it a
valid configuration per the h/w specs which it just happens only Calxeda
implemented?

Unless it's a h/w bug I don't see why it couldn't go upstream first.
Even if it is it might still stand a chance.

> If so, Calxeda server won't be able to use properly SMMU.
> 
> Even though the server will never be used, I do all my SMMU development
> on it.

The fact that Calxeda are no longer around doesn't in itself preclude
getting these patches upstreamed. After all, no one is deleting CX
support and some people do have them (not just us). It's hardly the most
obscure platform supported by Linux...

Ian.


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