On 15.02.2022 15:02, 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.
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.
