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

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Message-ID: <20250721200926.GA1179079-robh@kernel.org>
Date: Mon, 21 Jul 2025 15:09:26 -0500
From: Rob Herring <robh@...nel.org>
To: Clément Le Goffic <clement.legoffic@...s.st.com>
Cc: Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	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 v2 05/16] dt-bindings: memory: add jedec,ddr[3-4]-channel
 binding

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@...s.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@...il.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.

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

Rob