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

On 15.02.2022 15:02, Michal Simek wrote:

On 2/15/22 14:49, Rafał Miłecki wrote:

...

From: Rafał Miłecki rafal@milecki.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@milecki.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@milecki.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.

We'll need to find some consensus considering all points: 1. DT objectives 2. U-Boot needs 3. Linux needs

DT should mainly describe hardware / platform without focusing on a single implementation details. If U-Boot env data is indeed stored in a flash block (or blocks) / UBI volume, its binding should be just that.

If U-Boot requires MTD to parse proposed binding and it can't be afforded at the same time - maybe it can come with different implementation?

I think the way how I think this can be handled is.

One minor note: I don't think you can have one "standard" format and one "redundant" format. If env data is stored in two places - both use the redundant format.

# 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>;

1. Using &qspi seems reundant here, you can get parent flash device by walking DT. 2. Using "chosen" seems to be a /shortcut/ for getting env data location, I don't see any direct conflict with using "compatible" string as proposed in my binding.

#or         u-boot,env = <&qspi 0 40000>;         u-boot,env-redundant = <&qspi 40000 40000>;

Here you moved code describing partition from "partitions" into "chosen" which seems incorrect to me. We already have bindings for partitions and they should be children of flash node.

#or         u-boot,env = <&mmc 0 0 10000>; #device/start/size - raw mode         u-boot,env = <&mmc 0 1>; # device/partition - as file to FS         #etc.     }; };

&qspi {     flash {         partitions {             compatible = "fixed-partitions";             #address-cells = <1>;             #size-cells = <1>;

part0: partition@0 {                 label = "u-boot-env";                 reg = <0x0 0x40000>;             };

part1: partition@40000 {                 label = "u-boot-env-redundant";                 reg = <0x40000 0x10000>;             };     }; };

So my summary for this would be: 1. Let's use partitions for placing env data partition binding 2. Let's add minimal U-Boot setup into "chosen" if needed

Please consider this:

chosen { u-boot { u-boot,env = <&env0>, <&env1>; }; };

&qspi { flash { partitions { compatible = "fixed-partitions"; #address-cells = <1>; #size-cells = <1>;

env0: partition@0 { label = "u-boot-env"; reg = <0x0 0x40000>; };

env1: partition@40000 { label = "u-boot-env-redundant"; reg = <0x40000 0x10000>; }; }; };

If you still need to access flash content directly, you can pretty easily calculate offset from &env0 and &env1 nodes.