Re: [PATCH v2 05/16] dt-bindings: memory: add jedec,ddr[3-4]-channel binding

[Clement LE GOFFIC <clement.legoffic@foss.st.com>]

Hi Rob,

On 7/21/25 22:09, Rob Herring wrote:
> On Fri, Jul 11, 2025 at 04:48:57PM +0200, Clément Le Goffic wrote:
>> Introduce as per jedec,lpddrX-channel binding, jdec,ddr[3-4]-channel
>> binding.
>>
>> Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com>
>> ---
>>   .../memory-controllers/ddr/jedec,ddr-channel.yaml  | 53 ++++++++++++++++++++++
>>   1 file changed, 53 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/memory-controllers/ddr/jedec,ddr-channel.yaml b/Documentation/devicetree/bindings/memory-controllers/ddr/jedec,ddr-channel.yaml
>> new file mode 100644
>> index 000000000000..31daa22bcd4a
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/memory-controllers/ddr/jedec,ddr-channel.yaml
>> @@ -0,0 +1,53 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/memory-controllers/ddr/jedec,ddr-channel.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: DDR channel with chip/rank topology description
>> +
>> +description:
>> +  A DDR channel is a logical grouping of memory chips that are connected
>> +  to a host system. The main purpose of this node is to describe the
>> +  overall DDR topology of the system, including the amount of individual
>> +  DDR chips.
>> +
>> +maintainers:
>> +  - Clément Le Goffic <legoffic.clement@gmail.com>
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - jedec,ddr3-channel
>> +      - jedec,ddr4-channel
>> +
>> +  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 DDR 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 DDR chip, times the io-width of the channel divided by
>> +      the io-width of the DDR chip.
>> +    enum:
>> +      - 8
>> +      - 16
>> +      - 32
>> +      - 64
>> +      - 128
> 
> This is duplicating what's in jedec,lpddr-channel.yaml. Refactor or add
> to it rather than duplicating.

Yes I wanted something unique as "jedec,lpddr-channel.yaml" is 
specifically for lpddr.
I think I'll refactor and rename it "jedec,memory-channel.yaml" so it is 
more generic.

> Is there some reason regular DDR3/4 doesn't have ranks? I'm pretty sure
> it can...

Yes it does but I wasn't needing it and they are not required in case of 
lpddr. It will be fixed by refactoring jedec,lpddr-channel.yaml binding.

Best regards,
Clément