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

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Message-ID: <9417218b-6eda-373b-a2cb-869089ffc7cd@arm.com>
Date:   Mon, 25 Jan 2021 22:20:52 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Rob Herring <robh@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        mathieu.poirier@...aro.org, mike.leach@...aro.org,
        Linu Cherian <lcherian@...vell.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH V2 06/11] dts: bindings: Document device tree bindings for
 ETE

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@....com>
>>
>> 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@...r.kernel.org
>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>> Cc: Mike Leach <mike.leach@...aro.org>
>> Cc: Rob Herring <robh@...nel.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>   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@....com>
>> +  - Mathieu Poirier <mathieu.poirier@...aro.org>
>> +
>> +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