Re: [PATCH v3] dt-bindings: riscv: add SBI PMU event mappings

[Conor Dooley <conor@kernel.org>]

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Drew, Atish,

Mainly just a question about the OpenSBI doc at the end. Gonna fix up
the rest of the wording and resend in a few.

On Tue, Jan 03, 2023 at 10:28:16AM +0100, Andrew Jones wrote:
> On Mon, Jan 02, 2023 at 04:55:51PM +0000, Conor Dooley wrote:
> > From: Conor Dooley <conor.dooley@microchip.com>
> > 
> > The SBI PMU extension requires a firmware to be aware of the event to
> > counter/mhpmevent mappings supported by the hardware. OpenSBI may use
> > DeviceTree to describe the PMU mappings. This binding is currently
> > described in markdown in OpenSBI (since v1.0 in Dec 2021) & used by QEMU
> > since v7.2.0.
> > 
> > Import the binding for use while validating dtb dumps from QEMU and
> > upcoming hardware (eg JH7110 SoC) that will make use of the event
> > mapping.
> > 
> > Link: https://github.com/riscv-software-src/opensbi/blob/master/docs/pmu_support.md
> > Link: https://github.com/riscv-non-isa/riscv-sbi-doc/blob/master/riscv-sbi.adoc # Performance Monitoring Unit Extension
> > Co-developed-by: Atish Patra <atishp@rivosinc.com>
> > Signed-off-by: Atish Patra <atishp@rivosinc.com>
> > Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

> > +  riscv,event-to-mhpmevent:
> > +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> > +    description:
> > +      Represents an ONE-to-ONE mapping between a PMU event and the event
> > +      selector value that platform expects to be written to the MHPMEVENTx CSR
>                             ^ the

I think this one is arguable, it makes sense both ways IMO. I don't care
since it's not my prose though ;)

> > +      for that event.
> > +      The mapping is encoded in an matrix format where each element represents
> > +      an event.
> > +      This property shouldn't encode any raw hardware event.
> > +    items:
> > +      items:
> > +        - description: event_idx, a 20-bit wide encoding of the event type and
> > +            code. Refer to the SBI specification for a complete description of
> > +            the event types and codes.
> > +        - description: upper 32 bits of the event selector value for MHPMEVENTx
> > +        - description: lower 32 bits of the event selector value for MHPMEVENTx
> 
> > +     * codes, U74 uses a bitfield for events encoding, so several U74 events
> > +     * can be bound to single perf id.
>                                 ^ a   ID
> 
> > +     * See SBI PMU hardware id's in OpenSBI's include/sbi/sbi_ecall_interface.h
> 
> IDs

Most of this stuff comes directly from the doc in OpenSBI that I
copy-pasted. Atish, what do you wanna do once the binding is upstream
about the original doc?

Thanks,
Conor.


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