linux-kernel - Re: [RFC PATCH 1/2] dt-bindings: mtd: Add bindings for describing concatinated MTD devices

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Message-ID: <87frnoy8na.fsf@bootlin.com>
Date: Mon, 18 Nov 2024 14:27:21 +0100
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>
Cc: <tudor.ambarus@...aro.org>,  <michael@...le.cc>,  <broonie@...nel.org>,
  <pratyush@...nel.org>,  <richard@....at>,  <vigneshr@...com>,
  <robh@...nel.org>,  <conor+dt@...nel.org>,  <krzk+dt@...nel.org>,
  <venkatesh.abbarapu@....com>,  <linux-spi@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>,  <linux-mtd@...ts.infradead.org>,
  <nicolas.ferre@...rochip.com>,  <alexandre.belloni@...tlin.com>,
  <claudiu.beznea@...on.dev>,  <michal.simek@....com>,
  <linux-arm-kernel@...ts.infradead.org>,  <alsa-devel@...a-project.org>,
  <patches@...nsource.cirrus.com>,  <git@....com>,
  <amitrkcian2002@...il.com>,  <beanhuo@...ron.com>
Subject: Re: [RFC PATCH 1/2] dt-bindings: mtd: Add bindings for describing
 concatinated MTD devices

On 26/10/2024 at 13:23:46 +0530, Amit Kumar Mahapatra <amit.kumar-mahapatra@....com> wrote:

> This approach was suggested by Rob [1] during a discussion on Miquel's
> initial approach [2] to extend the MTD-CONCAT driver to support stacked
> memories.
> Define each flash node separately with its respective partitions, and add
> a 'concat-parts' binding to link the partitions of the two flash nodes that
> need to be concatenated.
>
> flash@0 {
>         compatible = "jedec,spi-nor"
>         ...
>                 partitions {

Wrong indentation here and below which makes the example hard to read.

>                 compatible = "fixed-partitions";
>                         concat-partition = <&flash0_partition &flash1_partition>;
>                         flash0_partition: partition@0 {
>                                 label = "part0_0";
>                                 reg = <0x0 0x800000>;
>                         }
>                 }
> }
> flash@1 {
>         compatible = "jedec,spi-nor"
>         ...
>                 partitions {
>                 compatible = "fixed-partitions";
>                         concat-partition = <&flash0_partition &flash1_partition>;
>                         flash1_partition: partition@0 {
>                                 label = "part0_1";
>                                 reg = <0x0 0x800000>;
>                         }
>                 }
> }

This approach has a limitation I didn't think about before: you cannot
use anything else than fixed partitions as partition parser.

> Based on the bindings the MTD-CONCAT driver need to be updated to create
> virtual mtd-concat devices.
>
> [1] https://lore.kernel.org/all/20191118221341.GA30937@bogus/
> [2] https://lore.kernel.org/all/20191113171505.26128-4-miquel.raynal@bootlin.com/
>
> Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>
> ---
>  .../mtd/partitions/fixed-partitions.yaml       | 18 ++++++++++++++++++
>  .../bindings/mtd/partitions/partitions.yaml    |  6 ++++++
>  2 files changed, 24 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml b/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml
> index 058253d6d889..df4ccb3dfeba 100644
> --- a/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml
> +++ b/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml
> @@ -183,3 +183,21 @@ examples:
>              read-only;
>          };
>      };
> +
> +  - |
> +    partitions {
> +        compatible = "fixed-partitions";
> +        #address-cells = <1>;
> +        #size-cells = <1>;

This is not strictly related but I believe we will soon have issues with
these, as we will soon cross the 4GiB boundary.

> +        concat-parts = <&part0 &part1>;
> +
> +        part0: partition@0 {
> +            label = "flash0-part0";
> +            reg = <0x0000000 0x100000>;
> +        };
> +
> +        part1: partition@...000 {
> +            label = "flash1-part0";
> +            reg = <0x0100000 0x200000>;
> +        };
> +    };
> diff --git a/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml b/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml
> index 1dda2c80747b..86bbd83c3f6d 100644
> --- a/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml
> +++ b/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml
> @@ -32,6 +32,12 @@ properties:
>    '#size-cells':
>      enum: [1, 2]
>  
> +  concat-parts:
> +    description: List of MTD partitions phandles that should be concatenated.
> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> +    minItems: 2
> +    maxItems: 4
> +
>  patternProperties:
>    "^partition(-.+|@[0-9a-f]+)$":
>      $ref: partition.yaml

Fine by me otherwise.

Thanks,
Miquèl