Re: [PATCH V2 06/11] dts: bindings: Document device tree bindings for ETE

[Suzuki K Poulose]

Hi Rob

On 1/25/21 7:22 PM, Rob Herring wrote:
> On Wed, Jan 13, 2021 at 09:48:13AM +0530, Anshuman Khandual wrote:
> > From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> >
> > Document the device tree bindings for Embedded Trace Extensions.
> > ETE can be connected to legacy coresight components and thus
> > could optionally contain a connection graph as described by
> > the CoreSight bindings.
> >
> > Cc: devicetree@xxxxxxxxxxxxxxx
> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> > Cc: Rob Herring <robh@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > ---
> >   Documentation/devicetree/bindings/arm/ete.yaml | 71 ++++++++++++++++++++++++++
> >   1 file changed, 71 insertions(+)
> >   create mode 100644 Documentation/devicetree/bindings/arm/ete.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/arm/ete.yaml b/Documentation/devicetree/bindings/arm/ete.yaml
> > new file mode 100644
> > index 0000000..00e6a77
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/arm/ete.yaml
> > @@ -0,0 +1,71 @@
> > +# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
> > +# Copyright 2021, Arm Ltd
> > +%YAML 1.2
> > +---
> > +$id: "http://devicetree.org/schemas/arm/ete.yaml#";
> > +$schema: "http://devicetree.org/meta-schemas/core.yaml#";
> > +
> > +title: ARM Embedded Trace Extensions
> > +
> > +maintainers:
> > +  - Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > +  - Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > +
> > +description: |
> > +  Arm Embedded Trace Extension(ETE) is a per CPU trace component that
> > +  allows tracing the CPU execution. It overlaps with the CoreSight ETMv4
> > +  architecture and has extended support for future architecture changes.
> > +  The trace generated by the ETE could be stored via legacy CoreSight
> > +  components (e.g, TMC-ETR) or other means (e.g, using a per CPU buffer
> > +  Arm Trace Buffer Extension (TRBE)). Since the ETE can be connected to
> > +  legacy CoreSight components, a node must be listed per instance, along
> > +  with any optional connection graph as per the coresight bindings.
> > +  See bindings/arm/coresight.txt.
> > +
> > +properties:
> > +  $nodename:
> > +    pattern: "^ete([0-9a-f]+)$"
> > +  compatible:
> > +    items:
> > +      - const: arm,embedded-trace-extension
> > +
> > +  cpu:
>
> We use 'cpus' in a couple of other places, let's do that here for
> consistency.

This is following the existing CoreSight bindings for ETM. The same driver
probes both. Also there can only ever be a single CPU for ete/etm. So, we
would prefer to keep it aligned with the existing bindings to avoid causing
confusion.

> > +    description: |
> > +      Handle to the cpu this ETE is bound to.
> > +    $ref: /schemas/types.yaml#/definitions/phandle
> > +
> > +  out-ports:
> > +    description: |
> > +      Out put connections from the ETE to legacy CoreSight trace bus.
>
> Output

Will fix.

> > +    $ref: /schemas/graph.yaml#/properties/ports
>
> You have to define what each 'port' is if there can be more than 1. If
> there's only ever 1 then you just need 'port' though maybe all the
> coresight bindings require 'out-ports'. And the port nodes need a $ref
> to '/schemas/graph.yaml#/properties/port'.

All CoreSight components require an out-ports and/or in-ports. The ETM/ETE
always has one port, but must be under out-ports in line with the CoreSight
bindings.

Does this look more apt:

   out-ports:
     description: |
       Output connection from the ETE to legacy CoreSight trace bus.
     poperties:
        port:
          $ref: /schemas/graph.yaml#/properties/port

Suzuki