linux-kernel - Re: [PATCH v3 2/3] dt-bindings: arm: Add Coresight Dummy Trace

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Date:   Fri, 28 Apr 2023 15:09:43 +0800
From:   Hao Zhang <quic_hazha@...cinc.com>
To:     Rob Herring <robh@...nel.org>
CC:     Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Konrad Dybcio <konradybcio@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <coresight@...ts.linaro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        Tingwei Zhang <quic_tingweiz@...cinc.com>,
        Jinlong Mao <quic_jinlmao@...cinc.com>,
        "Yuanfang Zhang" <quic_yuanfang@...cinc.com>,
        Tao Zhang <quic_taozha@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>,
        "Bjorn Andersson" <andersson@...nel.org>,
        <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] dt-bindings: arm: Add Coresight Dummy Trace

Hi Rob,

On 4/26/2023 2:46 AM, Rob Herring wrote:
> On Sat, Apr 22, 2023 at 03:37:13PM +0800, Hao Zhang wrote:
>> Add new coresight-dummy.yaml file describing the bindings required
>> to define coresight dummy trace in the device trees.
>>
>> Signed-off-by: Hao Zhang <quic_hazha@...cinc.com>
>> ---
>>   .../bindings/arm/arm,coresight-dummy.yaml     | 101 ++++++++++++++++++
>>   1 file changed, 101 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
>> new file mode 100644
>> index 000000000000..48d864aefaaa
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
>> @@ -0,0 +1,101 @@
>> +# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/arm/arm,coresight-dummy.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: ARM Coresight Dummy component
>> +
>> +description: |
>> +  Coresight Dummy Trace Module is for the specific devices that kernel
>> +  don't have permission to access or configure, e.g., CoreSight TPDMs
>> +  on Qualcomm platforms. So there need driver to register dummy devices
>> +  as Coresight devices. It may also be used to define components that
>> +  may not have any programming interfaces (e.g, static links), so that
>> +  paths can be established in the driver. Provide Coresight API for
>> +  dummy device operations, such as enabling and disabling dummy devices.
>> +  Build the Coresight path for dummy sink or dummy source for debugging.
>> +
>> +  The primary use case of the coresight dummy is to build path in kernel
>> +  side for dummy sink and dummy source.
> 
> I could imagine the OS wanting to know more information than just
> 'dummy'. Is data from an unknown source useful? Likewise, don't you want
> to know where you are sending data too?
> 
The necessary information for Coresight is connection between different 
components, so there is in-port for dummy sink and out-port for dummy 
source. We can get the whole path from the source to sink in device tree.

>> +
>> +maintainers:
>> +  - Mao Jinlong <quic_jinlmao@...cinc.com>
>> +  - Tao Zhang <quic_taozha@...cinc.com>
>> +  - Hao Zhang <quic_hazha@...cinc.com>
>> +
>> +properties:
>> +  compatible:
>> +    oneOf:
>> +      - enum:
> 
> Don't need oneOf as there is only one entry.
> 
OK, I will remove it in the next version of patch.
>> +          - arm,coresight-dummy-sink
>> +          - arm,coresight-dummy-source
>> +
>> +  out-ports:
>> +    $ref: /schemas/graph.yaml#/properties/ports
>> +
>> +    properties:
>> +      port:
>> +        description: Output connection from the source to Coresight
>> +          Trace bus.
>> +        $ref: /schemas/graph.yaml#/properties/port
>> +
>> +  in-ports:
>> +    $ref: /schemas/graph.yaml#/properties/ports
>> +
>> +    properties:
>> +      port:
>> +        description: Input connection from the Coresight Trace bus to
>> +          dummy sink, such as Embedded USB debugger(EUD).
>> +        $ref: /schemas/graph.yaml#/properties/port
>> +
>> +required:
>> +  - compatible
>> +
>> +if:
>> +  # If the compatible contains the below value
>> +  properties:
>> +    compatible:
>> +      contains:
>> +        const: arm,coresight-dummy-sink
>> +
>> +then:
>> +  required:
>> +    - in-ports
>> +
>> +else:
>> +  required:
>> +    - out-ports
> 
> This still allows the nodes when they don't make sense. I think this
> needs to be 2 schema files. The only common part is 'compatible' and
> that's not even shared.
>  > Rob
Dummy driver is very simple, the only goal of it is to build a path in 
kernel for subsystem, so we want to handle dummy source and sink in a 
generic framework.

Thanks,
Hao