On 09/22/2017 08:53 PM, Lorenzo Pieralisi wrote:

On Thu, Sep 21, 2017 at 09:17:17PM +0800, Hanjun Guo wrote:

quoted

From: Hanjun Guo <redacted>

IORT revision C introduced SMMUv3 MSI support which adding a
device ID mapping index in SMMUv3 sub table, to get the SMMUv3
device ID mapping for the output ID (dev ID for ITS) and the
link to which ITS.

So if a platform supports SMMUv3 MSI for control interrupt,
there will be a additional single map entry under SMMU, this
will not introduce any difference for devices just use one
step map to get its output ID and parent (ITS or SMMU), such
as PCI/NC/PMCG ---> ITS or PCI/NC ---> SMMU, but we need to
do the special handling for two steps map case such as
PCI/NC--->SMMUv3--->ITS.

Take a PCI hostbridge for example,

|----------------------|
|  Root Complex Node   |
|----------------------|
|    map entry[x]      |
|----------------------|
|       id value       |
| output_reference     |
|---|------------------|
     |
     |   |----------------------|
     |-->|        SMMUv3        |
         |----------------------|
         |     SMMU dev ID      |
         |     mapping index 0  |
         |----------------------|
         |      map entry[0]    |
         |----------------------|
         |       id value       |
         | output_reference-----------> ITS 1 (SMMU MSI domain)
         |----------------------|
         |      map entry[1]    |
         |----------------------|
         |       id value       |
         | output_reference-----------> ITS 2 (PCI MSI domain)
         |----------------------|

When the SMMU dev ID mapping index is 0, there is entry[0]
to map to a ITS, we need to skip that map entry for PCI
or NC (named component), or we may get the wrong ITS parent.

We do skip it because it is a single mapping that it is currently
not allowed for SMMUv3 components, right ?

Ok, we barf with a printk log message if we encounter such mapping
but the mapping won't resolve to the SMMUv3 MSI in the current
kernel.

This is not clear in the spec, maybe we also need to update the IORT
spec about it.

Thanks
Hanjun