linux-kernel - Re: [PATCH v4 05/20] dt-bindings: memory: factorise LPDDR props into SDRAM props

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Message-ID: <ce0cb3ba-2373-479f-a8f3-3a89ffb0a1b1@foss.st.com>
Date: Fri, 25 Jul 2025 09:06:33 +0200
From: Clement LE GOFFIC <clement.legoffic@...s.st.com>
To: Julius Werner <jwerner@...omium.org>
CC: Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
        Rob
 Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor
 Dooley <conor+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Philipp Zabel
	<p.zabel@...gutronix.de>,
        Jonathan Corbet <corbet@....net>,
        Gatien Chevallier
	<gatien.chevallier@...s.st.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Gabriel Fernandez
	<gabriel.fernandez@...s.st.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Le
 Goffic <legoffic.clement@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-perf-users@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v4 05/20] dt-bindings: memory: factorise LPDDR props into
 SDRAM props

Hi Julius,

On 7/25/25 00:33, Julius Werner wrote:
>>> I don't think this will identify a part unambiguously, I would expect
>>> the DDR revision ID to be specific to the part number. (In fact, we're
>>> also not sure whether manufacturer+revision identifies LPDDR parts
>>> unambiguously for every vendor, we just didn't have anything more to
>>> work with there.) I would suggest to use either `ddrX-YYYY,AAA...,ZZ`
>>> or `ddrX-YYYY,ZZ,AAA...` (where AAA... is the part number string from
>>> SPD 329-348 without the trailing spaces). The first version looks a
>>> bit more natural but it might get confusing on the off chance that
>>> someone uses a comma in a part number string.
>>
>> The first one seems better indeed.
>> If the manufacturer put a comma in the part number we should handle it
>> at a software level to me and if it is a devicetree error it is up to
>> the devicetree writer to fix it.
>> What do you think ?

I meant exactly what you are stating below :-)

> 
> Not sure what you mean by "handle it at a software level"? Using comma
> characters in the part number is not illegal according to the SPD
> spec, as far as I can tell.
> 
> That said, it is still possible to disambiguate this as long as the
> revision number is always there, you just have to look for the last
> comma from the end (so e.g. the string `ddr4-1234,some,part,567,89`
> could be unambiguously parsed as manufacturer ID 0x1234, part number
> `some,part,567` and revision ID 0x89, the parsing code just needs to
> be a bit careful). So maybe this is not actually a problem.

Best regards,
Clément