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The SMMUv3 spec has a note that BYPASS and ATS don't work together under
the STE EATS field definition. However there is another section "13.6.4
Full ATS skipping stage 1" that explains under certain conditions BYPASS
and ATS do work together if the STE is using S1DSS to select BYPASS and
the CD table has the possibility for a substream.
When these comments were written the understanding was that all forms of
BYPASS just didn't work and this was to be a future problem to solve.
It turns out that ATS and IDENTITY will always work just fine:
- If STE.Config = BYPASS then the PCI ATS is disabled
- If a PASID domain is attached then S1DSS = BYPASS and ATS will be
enabled. This meets the requirements of 13.6.4 to automatically
generate 1:1 ATS replies on the RID.
Update the comments to reflect this.
Fixes: 7497f4211f ("iommu/arm-smmu-v3: Make changing domains be hitless for ATS")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/0-v1-f27174f44f39+27a33-smmuv3_ats_note_jgg@nvidia.com
Signed-off-by: Will Deacon <will@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.