linux-kernel - Re: [PATCH] dt-bindings: dma: qcom,bam-dma: add optional memory interconnect properties

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Date:   Wed, 8 Feb 2023 10:08:20 +0100
From:   neil.armstrong@...aro.org
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: dma: qcom,bam-dma: add optional memory
 interconnect properties

On 08/02/2023 10:03, Krzysztof Kozlowski wrote:
> On 07/02/2023 16:27, Dmitry Baryshkov wrote:
>> On 07/02/2023 15:35, Neil Armstrong wrote:
>>> On 07/02/2023 11:32, Dmitry Baryshkov wrote:
>>>> On 07/02/2023 12:03, Neil Armstrong wrote:
>>>>> Recents SoCs like the SM8450 or SM8550 requires memory interconnect
>>>>> in order to have functional DMA.
>>>>>
>>>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>>>>> ---
>>>>>    Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml | 6 ++++++
>>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> I suspect this will not work without a change for a driver.
>>>>
>>>
>>> I had the impression single interconnect entries would be taken in account
>>> by the platform core, but it doesn't seem to be the case, anyway I can;t
>>> find
>>> any code doing that.
>>
>> Probably you mixed interconnects and power-domains here.
>>
> 
> The driver change was submitted some time ago:
> https://lore.kernel.org/all/20210505213731.538612-10-bhupesh.sharma@linaro.org/
> 
> There is already DTS user of it and we expect driver to be resubmitted
> at some point.
> 
> What I don't really get is that crypto driver sets bandwidth for
> interconnects, not the BAM. Why BAM needs interconnect? Usually you do
> not need to initialize some middle paths. Getting the final interconnect
> path (e.g. crypto-memory) is enough, because it includes everything in
> between.

Indeed the interconnect on BAM may be redundant since QCE sets the BW,
I'll investigate to understand if it's also necessary on BAM.

Neil

> 
> Maybe my review tag was a bit premature...
> 
> Best regards,
> Krzysztof
>