Re: [PATCH v4 2/3] spi: dt-bindings: Describe stacked/parallel memories modes

From: Rob Herring <robh@kernel.org>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Tudor Ambarus <Tudor.Ambarus@microchip.com>,
	Pratyush Yadav <p.yadav@ti.com>, Michael Walle <michael@walle.cc>,
	linux-mtd@lists.infradead.org, Michal Simek <monstr@monstr.eu>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	devicetree@vger.kernel.org, Mark Brown <broonie@kernel.org>,
	linux-spi@vger.kernel.org
Subject: Re: [PATCH v4 2/3] spi: dt-bindings: Describe stacked/parallel memories modes
Date: Tue, 14 Dec 2021 11:32:56 -0600	[thread overview]
Message-ID: <YbjVSNAC8M5Y1nHp@robh.at.kernel.org> (raw)
In-Reply-To: <20211210201039.729961-3-miquel.raynal@bootlin.com>

On Fri, Dec 10, 2021 at 09:10:38PM +0100, Miquel Raynal wrote:
> Describe two new memories modes:
> - A stacked mode when the bus is common but the address space extended
>   with an additinals wires.
> - A parallel mode with parallel busses accessing parallel flashes where
>   the data is spread.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> ---
>  .../bindings/spi/spi-peripheral-props.yaml    | 29 +++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
> index 5dd209206e88..4194fee8f556 100644
> --- a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
> +++ b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
> @@ -82,6 +82,35 @@ properties:
>      description:
>        Delay, in microseconds, after a write transfer.
>  
> +  stacked-memories:
> +    $ref: /schemas/types.yaml#/definitions/uint64-matrix

matrix or...

> +    description: Several SPI memories can be wired in stacked mode.
> +      This basically means that either a device features several chip
> +      selects, or that different devices must be seen as a single
> +      bigger chip. This basically doubles (or more) the total address
> +      space with only a single additional wire, while still needing
> +      to repeat the commands when crossing a chip boundary. The size of
> +      each chip should be provided as members of the array.

array?

Sounds like an array from the description as there is only 1 element, 
the size.

> +    minItems: 2
> +    maxItems: 2
> +    items:
> +      maxItems: 1

This says you can only have 2 64-bit entries. Probably not what you 
want. This looks like a case for a maxItems 'should be enough for now' 
type of value.

> +
> +  parallel-memories:
> +    $ref: /schemas/types.yaml#/definitions/uint64-matrix
> +    description: Several SPI memories can be wired in parallel mode.
> +      The devices are physically on a different buses but will always
> +      act synchronously as each data word is spread across the
> +      different memories (eg. even bits are stored in one memory, odd
> +      bits in the other). This basically doubles the address space and
> +      the throughput while greatly complexifying the wiring because as
> +      many busses as devices must be wired. The size of each chip should
> +      be provided as members of the array.
> +    minItems: 2
> +    maxItems: 2
> +    items:
> +      maxItems: 1
> +
>  # The controller specific properties go here.
>  allOf:
>    - $ref: cdns,qspi-nor-peripheral-props.yaml#
> -- 
> 2.27.0
> 
> 

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