linux-kernel - Re: [PATCH v6 1/4] dt-bindings: interconnect: qcom,msm8998-cpu-bwmon: add BWMON device

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Date:   Thu, 30 Jun 2022 13:23:49 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Rajendra Nayak <quic_rjendra@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Georgi Djakov <djakov@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v6 1/4] dt-bindings: interconnect: qcom,msm8998-cpu-bwmon:
 add BWMON device

On 30/06/2022 13:14, Rajendra Nayak wrote:
> 
> On 6/29/2022 7:32 PM, Krzysztof Kozlowski wrote:
>> Add bindings for the Qualcomm Bandwidth Monitor device providing
>> performance data on interconnects.  The bindings describe only BWMON CPU
>> (version 4), e.g. the instance which appeared for the first on Qualcomm
>> MSM8998 SoC and is also used on SDM845.  This BWMON device sits between
>> CPU and Last Level Cache Controller.
>>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> Reviewed-by: Rob Herring <robh@...nel.org>
>> Acked-by: Georgi Djakov <djakov@...nel.org>
>> ---
>>   .../interconnect/qcom,msm8998-llcc-bwmon.yaml | 85 +++++++++++++++++++
>>   1 file changed, 85 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/interconnect/qcom,msm8998-llcc-bwmon.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/interconnect/qcom,msm8998-llcc-bwmon.yaml b/Documentation/devicetree/bindings/interconnect/qcom,msm8998-llcc-bwmon.yaml
>> new file mode 100644
>> index 000000000000..76e09658d615
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/interconnect/qcom,msm8998-llcc-bwmon.yaml
>> @@ -0,0 +1,85 @@
>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/interconnect/qcom,msm8998-llcc-bwmon.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Qualcomm Interconnect Bandwidth Monitor
>> +
>> +maintainers:
>> +  - Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> +
>> +description: |
>> +  Bandwidth Monitor measures current throughput on buses between various NoC
>> +  fabrics and provides information when it crosses configured thresholds.
>> +
>> +  Certain SoCs might have more than one Bandwidth Monitors, for example on SDM845::
>> +   - Measuring the bandwidth between CPUs and Last Level Cache Controller -
>> +     called LLCC BWMON,
>> +   - Measuring the bandwidth between Last Level Cache Controller and memory (DDR).
>> +
>> +properties:
>> +  compatible:
>> +    oneOf:
>> +      - items:
>> +          - enum:
>> +              - qcom,sdm845-llcc-bwmon
>> +          - const: qcom,msm8998-llcc-bwmon
>> +      - const: qcom,msm8998-llcc-bwmon       # BWMON v4
>> +
>> +  interconnects:
>> +    maxItems: 1
>> +
>> +  interrupts:
>> +    maxItems: 1
>> +
>> +  operating-points-v2: true
>> +  opp-table: true
>> +
>> +  reg:
>> +    # BWMON v4 (currently described) and BWMON v5 use one register address
>> +    # space.  BWMON v2 uses two register spaces - not yet described.
>> +    maxItems: 1
>> +
>> +required:
>> +  - compatible
>> +  - interconnects
>> +  - interrupts
>> +  - operating-points-v2
>> +  - opp-table
>> +  - reg
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/interconnect/qcom,sdm845.h>
>> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
>> +
>> +    pmu@...6400 {
>> +        compatible = "qcom,sdm845-llcc-bwmon", "qcom,msm8998-llcc-bwmon";
> 
> so with this compatible fallback scheme, I am trying to understand what
> do I need to do if I have to add support for another SoC for instance.
> 
> I just update the binding with the new SoC compatible (lets say qcom,sc7280-llcc-bwmon)
> and in the device tree node use it as
> 	compatible = "qcom,sc7280-llcc-bwmon", "qcom,sdm845-llcc-bwmon", "qcom,msm8998-llcc-bwmon";
> without any updates in the driver?

I expect:
"qcom,sc7280-llcc-bwmon", "qcom,msm8998-llcc-bwmon";
and you need to add sc7280 compatible to the driver. The actual proper
solution in my patch would be to use msm8998 compatible in the driver,
but I did not test MSM8998.

Maybe we should switch to that anyway?

Best regards,
Krzysztof