linux-kernel - Re: [PATCH v4 1/4] dt-bindings: interconnect: qcom,sdm845-cpu-bwmon: add BWMON device

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Date:   Wed, 22 Jun 2022 17:28:50 +0530
From:   Rajendra Nayak <quic_rjendra@...cinc.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     Andy Gross <agross@...nel.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>,
        "Rob Herring" <robh@...nel.org>
Subject: Re: [PATCH v4 1/4] dt-bindings: interconnect: qcom,sdm845-cpu-bwmon:
 add BWMON device



On 6/7/2022 12:20 PM, Krzysztof Kozlowski wrote:
> On 06/06/2022 23:11, Bjorn Andersson wrote:
>> On Wed 01 Jun 03:11 PDT 2022, Krzysztof Kozlowski wrote:
>>
>>> Add bindings for the Qualcomm Bandwidth Monitor device providing
>>> performance data on interconnects.  The bindings describe only BWMON
>>> version 4, e.g. the instance on SDM845 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,sdm845-cpu-bwmon.yaml   | 97 +++++++++++++++++++
>>>   1 file changed, 97 insertions(+)
>>>   create mode 100644 Documentation/devicetree/bindings/interconnect/qcom,sdm845-cpu-bwmon.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/interconnect/qcom,sdm845-cpu-bwmon.yaml b/Documentation/devicetree/bindings/interconnect/qcom,sdm845-cpu-bwmon.yaml
>>> new file mode 100644
>>> index 000000000000..8c82e06ee432
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/interconnect/qcom,sdm845-cpu-bwmon.yaml
>>> @@ -0,0 +1,97 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/interconnect/qcom,sdm845-cpu-bwmon.yaml#
>>> +$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.
>>> +
>>> +properties:
>>> +  compatible:
>>> +    enum:
>>> +      - qcom,sdm845-cpu-bwmon       # BWMON v4
>>
>> It seems the thing that's called bwmon v4 is compatible with a number of
>> different platforms, should we add a generic compatible to the binding
>> as well, to avoid having to update the implementation for each SoC?
>>
>> (I.e. "qcom,sdm845-cpu-bwmon", "qcom,bwmon-v4")

it seems pretty useful to have the "qcom,bwmon-v4" and "qcom,bwmon-v5"
compatibles, I tried these patches on a sc7280 device which has a bwmon4
between the cpu and caches (and also has a bwmon5 between the caches and DDR)
and the driver works with zero changes.

> 
> I am hesitant. I could not find BWMON IP block versioning in the
> Qualcomm docs. Only the downstream sources had it. Therefore I think it
> is more applicable to use this one as fallback for other boards, e.g.:
> 
> "qcom,sdm660-cpu-bwmon", "qcom,sdm845-cpu-bwmon"
> (even if the number is a bit odd - newer comes as last compatible).
> 
> What's your preference?
> 
> Best regards,
> Krzysztof