Re: [PATCH 0/2] perf/smmuv3: Support devicetree

[Robin Murphy <robin.murphy@arm.com>]

On 2021-11-16 11:35, Jean-Philippe Brucker wrote:
> Add devicetree binding for the SMMUv3 PMU, called Performance Monitoring
> Counter Group (PMCG) in the spec. Each SMMUv3 implementation can have
> multiple independent PMCGs, for example one for the Translation Control
> Unit (TCU) and one per Translation Buffer Unit (TBU).
> 
> I previously sent the binding as reply to Jay Chen's thread implementing
> device tree support [1]. This posting addresses the comments from that
> thread.

Ha, I'd also resurrected this and was planning to post it at some point 
this week[0] - you should have said :)

> Patch 1 adds two compatible strings. "arm,smmu-v3-pmcg" is common to all
> PMCGs. "hisilicon,smmu-v3-pmcg-hip08" allows to support the same quirk
> as IORT for that implementation (see patch 2). We'll probably want to
> also introduce compatible strings for each implementation that has
> additional perf events. For example the MMU-600 implementation has
> different events for TCU and TBU PMCGs [2], but both components have the
> same device IDs. So the driver could differentiate them if they had two
> distinct compatible strings such as "arm,mmu-600-pmcg-tbu" and
> "arm,mmu-600-pmcg-tcu".

Actually it only needs a general MMU-600 compatible, since once you know 
it's an Arm Ltd. implementation, you can assume the pattern for the 
IMP_DEF ID registers to figure out the rest.

Robin.

[0] https://gitlab.arm.com/linux-arm/linux-rm/-/commits/smmu-pmcg

> The series doesn't deal with this because for testing I use a software
> model which only implements architected events. I do not include DTS
> change for that platform because enabling PMCGs requires an additional
> model option. See my branch smmu/pmu-dt [3] for details.
> 
> [1] https://lore.kernel.org/all/20200707150114.GC159413@myrica/
> [2] https://developer.arm.com/documentation/100310/0202/Functional-description/Operation/Performance-Monitoring-Unit
> [3] https://jpbrucker.net/git/linux/log/?h=smmu/pmu-dt
> 
> Jean-Philippe Brucker (2):
>    dt-bindings: Add Arm SMMUv3 PMCG binding
>    perf/smmuv3: Add devicetree support
> 
>   .../bindings/iommu/arm,smmu-v3-pmcg.yaml      | 67 +++++++++++++++++++
>   drivers/perf/arm_smmuv3_pmu.c                 | 25 ++++++-
>   2 files changed, 90 insertions(+), 2 deletions(-)
>   create mode 100644 Documentation/devicetree/bindings/iommu/arm,smmu-v3-pmcg.yaml
> 
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