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

On Wed, Mar 09, 2022 at 02:42:43PM +0100, Michal Simek wrote:

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.

It's always good to know what a node represents.

I would prefer to have just any link from u-boot node to partition instead.

That's a separate issue and having 'compatible' in no way disallows that.

Rob