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

Rafał Miłecki
2022-02-28T13:13:07Z

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>
--
2.34.1