Re: [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@xxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxx>
> > > ---
> > >   .../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@xxxxxxxxxx>
> > > +
> > > +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@xxxxxxxxx/
> 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