[RFC PATCH 1/6] dt-bindings: riscv: Add YAML documentation for PMU

[Anup Patel]

On Mon, Jun 29, 2020 at 12:06 PM Zong Li <zong.li at sifive.com> wrote:
>
> On Mon, Jun 29, 2020 at 12:38 PM Anup Patel <anup at brainfault.org> wrote:
> >
> > On Mon, Jun 29, 2020 at 9:58 AM Zong Li <zong.li at sifive.com> wrote:
> > >
> > > On Mon, Jun 29, 2020 at 12:09 PM Anup Patel <anup at brainfault.org> wrote:
> > > >
> > > > On Mon, Jun 29, 2020 at 8:49 AM Zong Li <zong.li at sifive.com> wrote:
> > > > >
> > > > > Add device tree bindings for performance monitor unit. And it passes the
> > > > > dt_binding_check verification.
> > > > >
> > > > > Signed-off-by: Zong Li <zong.li at sifive.com>
> > > > > ---
> > > > >  .../devicetree/bindings/riscv/pmu.yaml        | 59 +++++++++++++++++++
> > > > >  1 file changed, 59 insertions(+)
> > > > >  create mode 100644 Documentation/devicetree/bindings/riscv/pmu.yaml
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/riscv/pmu.yaml b/Documentation/devicetree/bindings/riscv/pmu.yaml
> > > > > new file mode 100644
> > > > > index 000000000000..f55ccbc6c685
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/riscv/pmu.yaml
> > > > > @@ -0,0 +1,59 @@
> > > > > +# SPDX-License-Identifier: GPL-2.0
> > > > > +%YAML 1.2
> > > > > +---
> > > > > +$id: http://devicetree.org/schemas/riscv/pmu.yaml#
> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > +
> > > > > +title: RISC-V Performance Monitor Units
> > > > > +
> > > > > +maintainers:
> > > > > +  - Zong Li <zong.li at sifive.com>
> > > > > +  - Paul Walmsley <paul.walmsley at sifive.com>
> > > > > +  - Palmer Dabbelt <palmer at dabbelt.com>
> > > > > +
> > > > > +properties:
> > > > > +  compatible:
> > > > > +    items:
> > > > > +      - const: riscv,pmu
> > > > > +
> > > > > +  riscv,width-base-cntr:
> > > > > +    description: The width of cycle and instret CSRs.
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > > +
> > > > > +  riscv,width-event-cntr:
> > > > > +    description: The width of hpmcounter CSRs.
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > >
> > > > The terms "base" and "event" is confusing because
> > > > we only have counters with no interrupt associated with it.
> > > >
> > > > The RISC-V spec defines 3 counters and rest are all
> > > > implementation specific counters.
> > >
> > > As I know, there are 2 counters of spec definition: cycle and instret.
> > > What is the 3rd counter you mentioned?
> >
> > TIME is a counter CSR.
> >
> > >
> > > >
> > > > I suggest using the terms "spec counters" and "impl counters"
> > > > instead of "base counters" and "event counters".
> > >
> > > OK, they are good to me. Let me change it.
> > >
> > >
> > > >
> > > > Further, "riscv,width" properties are redundant because
> > > > RISC-V spec clearly tells that counters are 64bit for both
> > > > RV32 and RV64.
> > > >
>
> Sorry for the lost replying. The maximum length of counters is 64, but
> it doesn't require to implement all bits. A real case is that
> unleashed board only implements 40 bit for mhpmcounters.

The "3.1.11 Hardware Performance Monitor" clearly states that
all counters are 64bit

To take care of the unleashed board, the "riscv,width-xyz" DT properties
should be optional. Whenever these properties are not present, we
should assume 64bit counter width.

>
> > > > > +
> > > > > +  riscv,n-event-cntr:
> > > > > +    description: The number of hpmcounter CSRs.
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > > +
> > > > > +  riscv,hw-event-map:
> > > > > +    description: The mapping of generic hardware events. Default is no mapping.
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > > > > +
> > > > > +  riscv,hw-cache-event-map:
> > > > > +    description: The mapping of generic hardware cache events.
> > > > > +      Default is no mapping.
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > > > > +
> > > > > +required:
> > > > > +  - compatible
> > > > > +  - riscv,width-base-cntr
> > > > > +  - riscv,width-event-cntr
> > > > > +  - riscv,n-event-cntr
> > > > > +
> > > > > +additionalProperties: false
> > > > > +
> > > > > +examples:
> > > > > +  - |
> > > > > +    pmu {
> > > > > +      compatible = "riscv,pmu";
> > > > > +      riscv,width-base-cntr = <64>;
> > > > > +      riscv,width-event-cntr = <40>;
> > > > > +      riscv,n-event-cntr = <2>;
> > > > > +      riscv,hw-event-map = <0x0 0x0 0x1 0x1 0x3 0x0202 0x4 0x4000>;
> > > > > +      riscv,hw-cache-event-map = <0x010201 0x0102 0x010204 0x0802>;
> > > > > +    };
> > > > > +
> > > > > +...
> > > > > --
> > > > > 2.27.0
> > > > >
> > > >
> > > > Regards,
> > > > Anup

Regards,
Anup