linux-kernel - Re: [PATCH net-next v2 1/3] dt-bindings: sram: qcom,imem: Allow modem-tables

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Message-ID: <f6b16d1d-3730-46d1-81aa-bfaf09c20754@oss.qualcomm.com>
Date: Thu, 31 Jul 2025 11:47:17 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller"
 <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Alex Elder <elder@...nel.org>
Cc: Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Alex Elder <elder@...cstar.com>
Subject: Re: [PATCH net-next v2 1/3] dt-bindings: sram: qcom,imem: Allow
 modem-tables

On 7/30/25 3:14 PM, Krzysztof Kozlowski wrote:
> On 30/07/2025 14:07, Konrad Dybcio wrote:
>>>>>>>
>>>>>>> Missing additionalProperties: false, which would point you that this is
>>>>>>> incomplete (or useless because empty).
>>>>>>
>>>>>> How do I describe a 'stupid' node that is just a reg?
>>>>> With "reg" - similarly to many syscon bindings.
>>>>
>>>> Is this sort of inline style acceptable, or should I introduce
>>>> a separate file?
>>>
>>> It's fine, assuming that it is desired in general. We do not describe
>>> individual memory regions of syscon nodes and this is a syscon.
>>>
>>> If this is NVMEM (which it looks like), then could use NVMEM bindings to
>>> describe its cells - individual regions. But otherwise we just don't.
>>
>> It's volatile on-chip memory
>>
>>> There are many exceptions in other platforms, mostly old or even
>>> unreviewed by DT maintainers, so they are not a recommended example.
>>>
>>> This would need serious justification WHY you need to describe the
>>> child. Why phandle to the main node is not enough for consumers.
>>
>> It's simply a region of the SRAM, which needs to be IOMMU-mapped in a
>> specific manner (should IMEM move away from syscon+simple-mfd to
>> mmio-sram?). Describing slices is the DT way to pass them (like under
>> NVMEM providers).
> 
> 
> Then this might be not a syscon, IMO. I don't think mixing syscon and
> SRAM is appropriate, even though Linux could treat it very similar.
> 
> syscon is for registers. mmio-sram is for SRAM or other parts of
> non-volatile RAM.
> 
> Indeed you might need to move towards mmio-sram.
> 
>>
>>>
>>> If the reason is - to instantiate child device driver - then as well no.
>>> This has been NAKed on the lists many times - you need resources if the
>>> child should be a separate node. Address space is one resource but not
>>> enough, because it can easily be obtained from the parent/main node.
>>
>> There is no additional driver for this
> 
> Then it is not a simple-mfd...

Indeed it's really not

I found out however that the computer history museum (i.e.
qcom-apq8064-asus-nexus7-flo.dts and qcom-msm8974.dtsi) seems to
have used simple-mfd, so that the subnode (syscon-reboot-mode) is
matched against a driver

The same can be achieved if we stick an of_platform_populate() at
the end of mmio-sram probe - thoughts?

Konrad