Message-ID: <e9e33fc7-4705-4e6d-bd33-ce9dc1a9b94e@foss.st.com>
Date: Wed, 23 Jul 2025 10:10:00 +0200
From: Clement LE GOFFIC <clement.legoffic@...s.st.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        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>,
        Le Goffic <legoffic.clement@...il.com>,
        Julius Werner <jwerner@...omium.org>,
        <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 v3 07/19] dt-bindings: memory: factorise LPDDR channel
 binding into memory channel

Hi Krzysztof,

On 7/23/25 08:57, Krzysztof Kozlowski wrote:
> On Tue, Jul 22, 2025 at 04:03:24PM +0200, Clément Le Goffic wrote:
>> LPDDR and DDR channels exist and share the same properties, they have a
>> compatible, ranks, and an io-width.
> 
> Maybe it is true for all types of SDRAM, like RDRAM and eDRAM, but I
> don't think all memory types do.
> 
> I think this should be renamed to sdram-channel.

Ok, do you want me to also the memory-props patch into sdram-props ?

> 
>>
>> Signed-off-by: Clément Le Goffic <clement.legoffic@...s.st.com>
>> ---
>>   ...pddr-channel.yaml => jedec,memory-channel.yaml} | 26 +++++++++++-----------
>>   1 file changed, 13 insertions(+), 13 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr-channel.yaml b/Documentation/devicetree/bindings/memory-controllers/ddr/jedec,memory-channel.yaml
>> similarity index 82%
>> rename from Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr-channel.yaml
>> rename to Documentation/devicetree/bindings/memory-controllers/ddr/jedec,memory-channel.yaml
>> index 34b5bd153f63..3bf3a63466eb 100644
>> --- a/Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr-channel.yaml
>> +++ b/Documentation/devicetree/bindings/memory-controllers/ddr/jedec,memory-channel.yaml
>> @@ -1,16 +1,16 @@
>>   # SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>   %YAML 1.2
>>   ---
>> -$id: http://devicetree.org/schemas/memory-controllers/ddr/jedec,lpddr-channel.yaml#
>> +$id: http://devicetree.org/schemas/memory-controllers/ddr/jedec,memory-channel.yaml#
>>   $schema: http://devicetree.org/meta-schemas/core.yaml#
>>   
>> -title: LPDDR channel with chip/rank topology description
>> +title: Memory channel with chip/rank topology description
>>   
>>   description:
>> -  An LPDDR channel is a completely independent set of LPDDR pins (DQ, CA, CS,
>> -  CK, etc.) that connect one or more LPDDR chips to a host system. The main
>> -  purpose of this node is to overall LPDDR topology of the system, including the
>> -  amount of individual LPDDR chips and the ranks per chip.
>> +  A memory channel is a completely independent set of pins (DQ, CA, CS,
> 
> A memory channel of SDRAM memory like DDR SDRAM or LPDDR SDRAM is ...

Ack

> 
>> +  CK, etc.) that connect one or more memory chips to a host system. The main
>> +  purpose of this node is to overall memory topology of the system, including the
>> +  amount of individual memory chips and the ranks per chip.
>>   
>>   maintainers:
>>     - Julius Werner <jwerner@...omium.org>
>> @@ -26,14 +26,14 @@ properties:
>>     io-width:
>>       description:
>>         The number of DQ pins in the channel. If this number is different
>> -      from (a multiple of) the io-width of the LPDDR chip, that means that
>> +      from (a multiple of) the io-width of the memory chip, that means that
>>         multiple instances of that type of chip are wired in parallel on this
>>         channel (with the channel's DQ pins split up between the different
>>         chips, and the CA, CS, etc. pins of the different chips all shorted
>>         together).  This means that the total physical memory controlled by a
>>         channel is equal to the sum of the densities of each rank on the
>> -      connected LPDDR chip, times the io-width of the channel divided by
>> -      the io-width of the LPDDR chip.
>> +      connected memory chip, times the io-width of the channel divided by
>> +      the io-width of the memory chip.
>>       enum:
>>         - 8
>>         - 16
>> @@ -51,8 +51,8 @@ patternProperties:
>>     "^rank@[0-9]+$":
>>       type: object
>>       description:
>> -      Each physical LPDDR chip may have one or more ranks. Ranks are
>> -      internal but fully independent sub-units of the chip. Each LPDDR bus
>> +      Each physical memory chip may have one or more ranks. Ranks are
>> +      internal but fully independent sub-units of the chip. Each memory bus
>>         transaction on the channel targets exactly one rank, based on the
>>         state of the CS pins. Different ranks may have different densities and
>>         timing requirements.
>> @@ -107,7 +107,7 @@ additionalProperties: false
>>   
>>   examples:
>>     - |
>> -    lpddr-channel0 {
>> +    memory-channel0 {
> 
> If doing this, then separate commit based on generic node name
> convention. But then we need to come with generic node name first,
> sdram-channel?

I don't want anything specific so yes it could be cool to have a generic 
node name.
"sdram-channel" is fine for me.
@Julius what do you think about it ?
Is your existing software generating it in the kernel ?
I'm curious about dynamic node name generation.

> 
> And also '-0', not '0' suffix.

Ack

> Best regards,
> Krzysztof
> 

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