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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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.



[Index of Archives]     [Device Tree Compilter]     [Device Tree Spec]     [Linux Driver Backports]     [Video for Linux]     [Linux USB Devel]     [Linux PCI Devel]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Yosemite Backpacking]


  Powered by Linux