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Re: [PATCH v3 0/3] Generic SMMU Bindings


On 02/02/2021 17:44, Stefano Stabellini wrote:
On Tue, 2 Feb 2021, Rahul Singh wrote:
Hello Stefano,

On 26 Jan 2021, at 10:58 pm, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:

Hi all,

This series introduces support for the generic SMMU bindings to

The last version of the series was

I realize that it is late for 4.15 -- I think it is OK if this series
goes in afterwards.

I tested the series on the Juno board it is woking fine.
I found one issue in SMMU driver while testing this series that is not related 
to this series but already existing issue in SMMU driver.

If there are more than one device behind SMMU and they share the same 
Stream-Id, SMMU driver is creating the new SMR entry without checking the 
already configured SMR entry if SMR entry correspond to stream-id is already 
configured.  Because of this I observed the stream match conflicts on Juno 

(XEN) smmu: /iommu@7fb30000: Unexpected global fault, this could be serious
(XEN) smmu: /iommu@7fb30000:    GFSR 0x00000004, GFSYNR0 0x00000006, GFSYNR1 
0x00000000, GFSYNR2 0x00000000

Below two patches is required to be ported to Xen to fix the issue from Linux 


Good catch and thanks for the pointers! Do you have any interest in
backporting these two patches or should I put them on my TODO list?

Unrelated to who does the job, we should discuss if it makes sense to
try to fix the bug for 4.15. The patches don't seem trivial so I am
tempted to say that it might be best to leave the bug unfixed for 4.15
and fix it later.

SMMU support on Juno is not that interesting because IIRC the stream-ID is the same for all the devices. So it is all or nothing passthrough.

For other HW, this may be a useful feature. Yet we would need a way to group the devices for passthrough.

In this context, I would consider it more a feature than a bug because the SMMU driver never remotely work on such HW.


Julien Grall



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