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Message-ID: <96f5a8d3-83db-fa1f-a27c-5c27d7c143e1@gmail.com>
Date: Mon, 28 Feb 2022 12:32:11 +0100
From: Rafał Miłecki <zajec5@...il.com>
To: Rob Herring <robh@...nel.org>
Cc: Tom Rini <trini@...sulko.com>,
Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
Ricardo Salveti <ricardo@...ndries.io>,
Michal Simek <michal.simek@...inx.com>,
Jorge Ramirez-Ortiz <jorge@...ndries.io>,
Sean Anderson <seanga2@...il.com>, devicetree@...r.kernel.org,
u-boot@...ts.denx.de, linux-kernel@...r.kernel.org,
Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH V2] dt-bindings: nvmem: add U-Boot environment variables
binding
On 25.02.2022 17:42, Rob Herring wrote:
> On Thu, Feb 17, 2022 at 02:02:35PM +0100, Rafał Miłecki wrote:
>> From: Rafał Miłecki <rafal@...ecki.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.
>
> How much of this is already in use vs. proposed? I know I've seen
> something, but that may have been a u-boot env string in 'label' and
> that's it.
[bootloader]
Right now U-Boot doesn't use any binding for describing env variables.
It's location is usually hardcoded, see (in U-Boot):
* CONFIG_ENV_ADDR
* CONFIG_ENV_SECT_SIZE
* CONFIG_ENV_ADDR_REDUND
[kernel]
There is no support for accessing U-Boot env data. This patch is the
first step for adding such a support.
[user-space]
OpenWrt uses bash script to store a list of devices and their U-Boot env
variables location. In a long term I'd like to replace it and use DT
info + possibly a kernel exposed NVMEM data.
>> 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@...ecki.pl>
>> ---
>> V2: Update descriptions to don't make this binding MTD (flash partition)
>> specific. Mention multiple possible storage ways.
>> ---
>> .../devicetree/bindings/nvmem/u-boot,env.yaml | 66 +++++++++++++++++++
>> MAINTAINERS | 5 ++
>> 2 files changed, 71 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..a53e34152c97
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
>> @@ -0,0 +1,66 @@
>> +# 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@...ecki.pl>
>> +
>> +allOf:
>> + - $ref: nvmem.yaml#
>
> What exactly is used from nvmem.yaml? Based on the example, nothing.
Nothing. I thought it's nice for a context. I'll drop it.
>> +
>> +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
>
> Aren't these 2 discoverable based on a flag or count property?
U-Boot discovers that based on a type of flash device(s). In redundant
mode env data can be stored on one or two flash devices.
U-Boot conditions:
/* Check flag scheme compatibility */
if (DEVTYPE(dev_current) == MTD_NORFLASH &&
DEVTYPE(!dev_current) == MTD_NORFLASH) {
environment.flag_scheme = FLAG_BOOLEAN;
} else if (DEVTYPE(dev_current) == MTD_NANDFLASH &&
DEVTYPE(!dev_current) == MTD_NANDFLASH) {
environment.flag_scheme = FLAG_INCREMENTAL;
} else if (DEVTYPE(dev_current) == MTD_DATAFLASH &&
DEVTYPE(!dev_current) == MTD_DATAFLASH) {
environment.flag_scheme = FLAG_BOOLEAN;
} else if (DEVTYPE(dev_current) == MTD_UBIVOLUME &&
DEVTYPE(!dev_current) == MTD_UBIVOLUME) {
environment.flag_scheme = FLAG_INCREMENTAL;
} else if (DEVTYPE(dev_current) == MTD_ABSENT &&
DEVTYPE(!dev_current) == MTD_ABSENT &&
IS_UBI(dev_current) == IS_UBI(!dev_current)) {
environment.flag_scheme = FLAG_INCREMENTAL;
} else {
fprintf(stderr, "Incompatible flash types!\n");
ret = -EINVAL;
goto open_cleanup;
}
I thought it's better & more flexible to describe format explicitly in
the DT. That way vendors have more options - they can e.g. start using
incremental setup on NOR flash devices.
>> +
>> + reg:
>> + maxItems: 1
>> +
>> +unevaluatedProperties: false
>> +
>> +examples:
>> + - |
>> + partitions {
>> + compatible = "fixed-partitions";
>> + #address-cells = <1>;
>> + #size-cells = <1>;
>> +
>> + partition@0 {
>> + reg = <0x0 0x40000>;
>> + label = "u-boot";
>> + read-only;
>> + };
>> +
>> + env: partition@...00 {
>> + compatible = "u-boot,env";
>> + reg = <0x40000 0x10000>;
>> + label = "u-boot-env";
>> + };
>> + };
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 66aa3a589f6a..55c56ce82856 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -19905,6 +19905,11 @@ 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@...ecki.pl>
>> +S: Maintained
>> +F: Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
>> +
>> UACCE ACCELERATOR FRAMEWORK
>> M: Zhangfei Gao <zhangfei.gao@...aro.org>
>> M: Zhou Wang <wangzhou1@...ilicon.com>
>> --
>> 2.34.1
>>
>>
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