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

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Message-ID: <e4c5ecc3-fd97-4b13-a057-bb1a3b7f9207@kernel.org>
Date: Wed, 30 Jul 2025 15:14:10 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 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 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...

Best regards,
Krzysztof