Re: [PATCH V3] dt-bindings: nvmem: add U-Boot environment variables binding

Michal Simek
2022-03-09T13:42:57Z

On 2/28/22 14:12, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@milecki.pl>
>
> U-Boot uses environment variables for storing device setup data. It
> usually needs to be accessed by a bootloader, kernel and often
> user-space.
>
> This binding allows describing environment data located in a raw flash
> partition. It's treated as NVMEM device and can be reused later for
> other storage devices.
>
> Using DT should be cleaner than hardcoding & duplicating such info in
> multiple places. Bootloader & kernel can share DTS and user-space can
> try reading it too or just have correct data exposed by a kernel.
>
> A custom "compatible" string allows system to automatically load
> relevant NVMEM driver but phandle can be also used for reading raw
> location.
>
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
> V2: Update descriptions to don't make this binding MTD (flash partition)
> specific. Mention multiple possible storage ways.
> V3: Drop
> allOf:
> - $ref: nvmem.yaml#
> as we don't use anything rom the nvmem.yaml. Thanks Rob.
> ---
> .../devicetree/bindings/nvmem/u-boot,env.yaml | 62 +++++++++++++++++++
> MAINTAINERS | 5 ++
> 2 files changed, 67 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
>
> diff --git a/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
> new file mode 100644
> index 000000000000..e70b2a60cb9a
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
> @@ -0,0 +1,62 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/nvmem/u-boot,env.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: U-Boot environment variables
> +
> +description: |
> + U-Boot uses environment variables to store device parameters and
> + configuration. They may be used for booting process, setup or keeping end user
> + info.
> +
> + Data is stored using U-Boot specific formats (variant specific header and NUL
> + separated key-value pairs).
> +
> + Environment data can be stored on various storage entities, e.g.:
> + 1. Raw flash partition
> + 2. UBI volume
> +
> + This binding allows marking storage device (as containing env data) and
> + specifying used format.
> +
> + Right now only flash partition case is covered but it may be extended to e.g.
> + UBI volumes in the future.
> +
> +maintainers:
> + - Rafał Miłecki <rafal@milecki.pl>
> +
> +properties:
> + compatible:
> + oneOf:
> + - description: A standalone env data block
> + const: u-boot,env
> + - description: Two redundant blocks with active one flagged
> + const: u-boot,env-redundant-bool
> + - description: Two redundant blocks with active having higher counter
> + const: u-boot,env-redundant-count
> +
> + reg:
> + maxItems: 1
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + partitions {
> + compatible = "fixed-partitions";
> + #address-cells = <1>;
> + #size-cells = <1>;
> +
> + partition@0 {
> + reg = <0x0 0x40000>;
> + label = "u-boot";
> + read-only;
> + };
> +
> + env: partition@40000 {
> + compatible = "u-boot,env";
> + reg = <0x40000 0x10000>;
> + };
> + };
> diff --git a/MAINTAINERS b/MAINTAINERS
> index db8052bc1d26..24fc181a7e6c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -19958,6 +19958,11 @@ W: http://linuxtv.org
> T: git git://linuxtv.org/media_tree.git
> F: drivers/media/pci/tw686x/
>
> +U-BOOT ENVIRONMENT VARIABLES
> +M: Rafał Miłecki <rafal@milecki.pl>
> +S: Maintained
> +F: Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
> +
> UACCE ACCELERATOR FRAMEWORK
> M: Zhangfei Gao <zhangfei.gao@linaro.org>
> M: Zhou Wang <wangzhou1@hisilicon.com>

I think that parsing these partitions is quite sw intensive process and I can't
still see the value to have compatible string here.
I would prefer to have just any link from u-boot node to partition instead.

But up to Simon or Tom to decide.

Thanks,
Michal