linux-kernel - Re: [PATCH v3 1/2] dt-bindings: soc: qcom: Add qcom,kaanapali-imem compatible

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Message-ID: <790ca394-cee2-412b-97d8-c6416b843010@oss.qualcomm.com>
Date: Tue, 4 Nov 2025 13:32:00 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Jingyi Wang <jingyi.wang@....qualcomm.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Robert Marko <robimarko@...il.com>,
        Das Srinagesh <quic_gurus@...cinc.com>, aiqun.yu@....qualcomm.com,
        tingwei.zhang@....qualcomm.com, trilok.soni@....qualcomm.com,
        yijie.yang@....qualcomm.com, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] dt-bindings: soc: qcom: Add qcom,kaanapali-imem
 compatible

On 11/4/25 9:16 AM, Krzysztof Kozlowski wrote:
> On Sun, Nov 02, 2025 at 11:25:06PM -0800, Jingyi Wang wrote:
>> Document qcom,kaanapali-imem compatible. Kaanapali IMEM is not a syscon or
>> simple-mfd, also "reboot reason" is not required on Kaanapali like some
> 
> I do not see correlation. Something is not a syscon, so you add a new
> generic compatible? No.
> 
>> other platforms. So define a common "qcom,imem" binding and fallback to it.
> 
> You did not define fallback to it!
> 
> ...
> 
>> +      - items:
>> +          - enum:
>> +              - qcom,kaanapali-imem
>> +          - const: qcom,imem
> 
> I do not understand what this generic compatible is supposed to express,
> not explained in commit msg. Considering this wasn't before, it is a
> major and really undesired change. It also makes no sesne. There was no
> generic compatible before but "if not syscon" now this must have generic
> compatible, what?

So IMEM (or SYSTEM_IMEM more specifically as opposed to BOOT_IMEM which
you can take your guesses what it's used for) is to the best of our
understanding just a piece of SRAM that's accessible by multiple
processors/subsystems on the SoC.

A smaller region within it ("shared IMEM") is a little bit of a dumping
ground for various (incl. runtime) configuration and debug magic data
and that's usually what Linux is concerned with.

IMEM is currently described as a simple-mfd+syscon, which it is clearly
not. The former, as we've established in the past, was used as a hack to
have something call of_platform_populate().

I think that in turn is only necessary for the old arm32 DTs which have
a syscon-reboot-mode node under IMEM (and I think that's where the syscon
compatible comes from).

Should we make the switch to mmio-sram and settle this discussion?
It would probably require convincing the sram maintainer to add that
of_platform_populate() call in its probe func and making syscon-reboot
not depend on a syscon (not like it's very hard)

Konrad