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

From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: Rob Herring <robh@kernel.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org,
	mathieu.poirier@linaro.org, mike.leach@linaro.org,
	Linu Cherian <lcherian@marvell.com>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH V2 06/11] dts: bindings: Document device tree bindings for ETE
Date: Mon, 25 Jan 2021 23:28:10 +0000	[thread overview]
Message-ID: <1528d7ce-6765-7adf-3e24-6da1a705331d@arm.com> (raw)
In-Reply-To: <9417218b-6eda-373b-a2cb-869089ffc7cd@arm.com>

On 1/25/21 10:20 PM, Suzuki K Poulose wrote:
> 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@arm.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@vger.kernel.org
>>> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
>>> Cc: Mike Leach <mike.leach@linaro.org>
>>> Cc: Rob Herring <robh@kernel.org>
>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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@arm.com>
>>> +  - Mathieu Poirier <mathieu.poirier@linaro.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

Correction, the above should be :

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

That works fine for me. Does that look fine ?  Some day, we should convert the
coresight dt bindings to yaml and import the out-ports/in-ports from the scheme :-)

Cheers
Suzuki