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

[Rob Herring]

On Thu, Mar 3, 2022 at 2:32 AM Rafał Miłecki <zajec5@xxxxxxxxx> 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.

That's what it is vs. what instance. You need a better example if
that's what you are trying to show. I guess if you were doing A/B
updates you'd have something like 'volume-name = "u-boot-env-b"'?

>
>
> > 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

Yes, it could be a human wanting to identify it. The question is
whether s/w does too.

The other aspect is there's also filesystem/partition label's. Those
are generally set by humans and opaque to the s/w. If the use is
aligned with how those labels are used, then I'd be okay with the DT
'label' here.

>
> ;) 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.

Maybe use "volume-$volumename" or "volume-$volumeid" instead?

Rob