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

Rafał Miłecki
2022-03-03T08:32:54Z

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