linux-kernel - Re: [PATCH V3 06/14] dts: bindings: Document device tree bindings for ETE

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Message-ID: <4d0e6b88-72c2-be23-f43a-3f541f9ebb86@arm.com>
Date:   Wed, 10 Feb 2021 12:33:44 +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,
        lcherian@...vell.com, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH V3 06/14] dts: bindings: Document device tree bindings for
 ETE

Hi Rob

On 2/9/21 7:00 PM, Rob Herring wrote:
> On Wed, Jan 27, 2021 at 02:25:30PM +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>
>> ---
>> Changes in V3:
>>
>> - Fixed all DT yaml semantics problems
>>
>>   Documentation/devicetree/bindings/arm/ete.yaml | 74 ++++++++++++++++++++++++++
>>   1 file changed, 74 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..edc1fe2
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/arm/ete.yaml
>> @@ -0,0 +1,74 @@
>> +# 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've already established 'cpus' for this purpose.
> 

Please see : https://lkml.kernel.org/r/9417218b-6eda-373b-a2cb-869089ffc7cd@arm.com
for my response in the previous version to this and the one with out-ports.

>> +    description: |
>> +      Handle to the cpu this ETE is bound to.
>> +    $ref: /schemas/types.yaml#/definitions/phandle
>> +
>> +  out-ports:
>> +    type: object
> 
> Replace with: $ref: /schemas/graph.yaml#/properties/ports

So, just to confirm again :
The CoreSight graph bindings expect the input ports and output ports
grouped under in-ports{} and out-ports{} respectively to avoid having
to specify the direction of the ports in the individual "port" nodes.
i.e

in-ports {

	property: ports
	  OR
	property: port

	required:
		OneOf:
			ports
			port
}

out-ports {

	# same as above
}

So thats why I added out-ports as a new object, where the ports/port
could be a child node.

Ideally the definition of out-ports /in-ports should go to a common schema
for CoreSight bindings, when we move to Yaml for the existing bindings,
which will follow in a separate series, later.

> 
>> +    description: |
>> +      Output connections from the ETE to legacy CoreSight trace bus.
>> +    properties:
>> +      port:
>> +        $ref: /schemas/graph.yaml#/properties/port
> 
> Actually, if only 1 port ever, you can drop 'out-ports' and just have
> 'port'. Not sure though if the coresight stuff depends on 'out-ports'.
> 

Cheers
Suzuki