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

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Date:   Wed, 8 Feb 2023 10:03:15 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        neil.armstrong@...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 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.

Maybe my review tag was a bit premature...

Best regards,
Krzysztof