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

[Michal Simek]

On 2/15/22 14:49, Rafał Miłecki wrote:
From: Rafał Miłecki <ra...@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 <ra...@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 <ra...@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.

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>;
                #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>;
                };
        };
};

Thanks,
Michal