[PATCH] dt-bindings: mtd: partitions: add UBI binding

[Rafał Miłecki]

Hi Rob, could you re-review my patch as I provided answers (see below), please?

On 3.03.2022 09:32, Rafał Miłecki wrote:
> 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 at 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 at 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 at 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 at 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