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Date:   Thu, 3 Mar 2022 09:32:41 +0100
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Subject: Re: [PATCH] dt-bindings: mtd: partitions: add UBI binding
To:     Rob Herring <robh@kernel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        linux-mtd@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, Tom Rini <trini@konsulko.com>,
        Ricardo Salveti <ricardo@foundries.io>,
        Michal Simek <michal.simek@xilinx.com>,
        Jorge Ramirez-Ortiz <jorge@foundries.io>,
        Sean Anderson <seanga2@gmail.com>, u-boot@lists.denx.de,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>
References: <20220217102448.27586-1-zajec5@gmail.com>
 <Yh/ovYMV104jc+CE@robh.at.kernel.org>
From:   =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>
In-Reply-To: <Yh/ovYMV104jc+CE@robh.at.kernel.org>
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On 2.03.2022 22:59, Rob Herring wrote:
> On Thu, Feb 17, 2022 at 11:24:48AM +0100, Rafał Miłecki wrote:
>> From: Rafał Miłecki <rafal@milecki.pl>
>>
>> UBI is often used on embedded devices to store UBI volumes with device
>> configuration / calibration data. Such volumes may need to be documented
>> and referenced for proper boot & setup.
>>
>> Some examples:
>> 1. U-Boot environment variables
>> 2. Device calibration data
>> 3. Default setup (e.g. initial password)
>>
>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>> ---
>>   .../bindings/mtd/partitions/ubi.yaml          | 67 +++++++++++++++++++
>>   1 file changed, 67 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/mtd/partitions/ubi.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/mtd/partitions/ubi.yaml b/Documentation/devicetree/bindings/mtd/partitions/ubi.yaml
>> new file mode 100644
>> index 000000000000..cd081f06d4cb
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/mtd/partitions/ubi.yaml
>> @@ -0,0 +1,67 @@
>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/mtd/partitions/ubi.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: UBI (Unsorted Block Images) device
>> +
>> +description: |
>> +  UBI is a layer providing logical volumes (consisting of logical blocks) on top
>> +  of raw flash devices. It deals with low-level flash issues (bit-flips, bad
>> +  physical eraseblocks, wearing) providing a reliable data storage.
>> +
>> +  UBI device is built and stored in a single flash partition.
>> +
>> +  Some (usually embedded) devices use UBI volumes of specific names or indexes
>> +  to store setup / configuration data. This binding allows describing such
>> +  volumes so they can be identified and referenced by consumers.
>> +
>> +maintainers:
>> +  - Rafał Miłecki <rafal@milecki.pl>
>> +
>> +allOf:
>> +  - $ref: partition.yaml#
>> +
>> +properties:
>> +  compatible:
>> +    const: ubi
>> +
>> +patternProperties:
>> +  "^volume-[0-9a-f]+$":
>> +    type: object
>> +    description: UBI volume
>> +    properties:
>> +      volume-name:
>> +        $ref: /schemas/types.yaml#/definitions/string
>> +      volume-id:
>> +        $ref: /schemas/types.yaml#/definitions/uint32
>> +    anyOf:
>> +      - required:
>> +          - volume-name
>> +      - required:
>> +          - volume-id
>> +
>> +unevaluatedProperties: false
>> +
>> +examples:
>> +  - |
>> +    partitions {
>> +        compatible = "fixed-partitions";
>> +        #address-cells = <1>;
>> +        #size-cells = <1>;
>> +
>> +        partition@0 {
>> +            compatible = "ubi";
>> +            reg = <0x0000000 0x1000000>;
>> +            label = "filesystem";
>> +
>> +            env: volume-0 {
>> +                volume-name = "u-boot-env";
> 
> Why not do 'compatible = "u-boot,env";' to align with normal partitions?

I mean to reserve "compatible" for describing UBI volume content.

If I manage to get
[PATCH V3] dt-bindings: nvmem: add U-Boot environment variables binding
https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20220228131250.16943-1-zajec5@gmail.com/
accepted, it'll allow me to later work on something like:

env: volume-0 {
     compatible = "u-boot,env";
     volume-name = "u-boot-env";
};

(I believe) I'll need (in the final shape) two properties:
1. One for describing UBI volume ("compatible")
2. One for identifying UBI volume ("volume-name" / "volume-id")

It's similar design to the "compatible" vs. "reg" in IO hw blocks.


> Or 'label'?

I could replace "volume-name" with "label" but someone once told me that:
 > 'label' is supposed to correspond to a sticker on a port or something
 > human identifiable

;) https://patchwork.ozlabs.org/comment/2812214/

So I don't want to abuse "label" here.


> We have enough ways to identify things, I don't think we need another.
> 
>> +            };
>> +
>> +            calibration: volume-1 {
> 
> Are 0 and 1 meaningful or just made up indexing?

Made up indexing. I need unique nodenames but @[0-9a-f] doesn't appply here.


>> +                volume-id = <99>;
>> +            };
>> +        };
>> +    };
>> -- 
>> 2.34.1