Re: [PATCH] dt-bindings: nvmem: add U-Boot environment variables binding
From: Michal Simek
Date: Wed Feb 16 2022 - 09:28:24 EST
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@xxxxxxxxxx>
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@xxxxxxxxxx>
---
.../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@xxxxxxxxxx>
+
+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