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

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Date:   Wed, 16 Feb 2022 15:28:06 +0100
From:   Michal Simek <michal.simek@...inx.com>
To:     Rafał Miłecki <zajec5@...il.com>,
        Sean Anderson <seanga2@...il.com>,
        Michal Simek <michal.simek@...inx.com>,
        Rob Herring <robh+dt@...nel.org>,
        Tom Rini <trini@...sulko.com>, Simon Glass <sjg@...omium.org>
CC:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Ricardo Salveti <ricardo@...ndries.io>,
        Jorge Ramirez-Ortiz <jorge@...ndries.io>,
        <devicetree@...r.kernel.org>, <u-boot@...ts.denx.de>,
        <linux-kernel@...r.kernel.org>,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH] dt-bindings: nvmem: add U-Boot environment variables
 binding



On 2/16/22 13:59, Rafał Miłecki wrote:
> On 15.02.2022 15:57, Sean Anderson wrote:
>> On 2/15/22 9:02 AM, Michal Simek wrote:
>>>
>>>
>>> On 2/15/22 14:49, Rafał Miłecki wrote:
>>>> From: Rafał Miłecki <rafal@...ecki.pl>
>>>>
>>>> U-Boot uses environment variables for storing device setup data on
>>>> flash. That data usually needs to be accessed by a bootloader, kernel
>>>> and often user-space.
>>>>
>>>> This binding allows describing environment data location and its format
>>>> clearly. In some/many cases it should be cleaner than hardcoding &
>>>> duplicating that 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.
>>>>
>>>> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
>>>> ---
>>>>   .../devicetree/bindings/nvmem/u-boot,env.yaml | 58 +++++++++++++++++++
>>>>   MAINTAINERS                                   |  5 ++
>>>>   2 files changed, 63 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..a2b3a9b88eb8
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
>>>> @@ -0,0 +1,58 @@
>>>> +# 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 on flash in a U-Boot specific format (header and NUL 
>>>> separated
>>>> +  key-value pairs).
>>>> +
>>>> +  This binding allows specifying data location and used format.
>>>> +
>>>> +maintainers:
>>>> +  - Rafał Miłecki <rafal@...ecki.pl>
>>>> +
>>>> +allOf:
>>>> +  - $ref: nvmem.yaml#
>>>> +
>>>> +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
>>>
>>> I am not convinced that this is the best way how to do it. Because in u-boot 
>>> implementation you would have to enable MTD partitions to get there.
>>> And the whole parsing will take a lot of time.
>>>
>>> I think the way how I think this can be handled is.
>>>
>>> # I don't think that discussion with Simon was finished.
>>> But for example (chosen or firmware node)
>>> chosen {
>>>      u-boot {
>>>          u-boot,env = <&qspi &part0>;
>>>          u-boot,env-redundant = <&qspi &part1>;
>>>          #or
>>>          u-boot,env = <&qspi 0 40000>;
>>>          u-boot,env-redundant = <&qspi 40000 40000>;
>>
>> What about when the environment is on top of UBI?
> 
> We can always add support for binding UBI volumes in DT. Somethig
> more-or-less like:
> 
> partitions {
>      compatible = "fixed-partitions";
>      #address-cells = <1>;
>      #size-cells = <1>;
> 
>      partition@0 {
>          compatible = "ubi";
>          label = "ubi";
>          reg = <0x0 0x1000000>;
> 
>          env0: partition-0 {
>              volume-name = "env";
>          };
> 
>          env1: partition-1 {
>              volume-id = <10>;
>          };
>      };
> };

If this is something ack by Rob I have no problem with it. But it has to go to 
schema.

M