On 7.03.2022 11:24, Alexander Dahl wrote:
Hei hei,
just want to give a little more background here from embedded non openwrt point of view. See below.
Am Mon, Feb 28, 2022 at 12:32:11PM +0100 schrieb Rafał Miłecki:
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@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.
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
And more … U-Boot has a variety of options to store the U-Boot env, from the top of my head:
- at some offset in raw flash / mtd partition on NAND, NOR, serial dataflash, etc.
- at some offset on a block device, e.g. on eMMC
- as a file in a FAT partition
- in a UBI volume
- …
And yes, it's determined by some build option and hardcoded at compile time.
[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.
U-Boot source itself has userspace tools fw_setenv and fw_printenv and those look into /etc/fw_env.config on how that env should be accessed.
I wasn't 100% clear on that but OpenWrt actually uses those U-Boot tools
OpenWrt scripts I mentioned can be found there: https://git.openwrt.org/?p=openwrt/openwrt.git;a=tree;f=package/boot/uboot-e...
Random example:
linksys,wrt1900ac-v1) ubootenv_add_uci_config "/dev/mtd1" "0x0" "0x40000" "0x20000" ;; linksys,wrt3200acm|\ linksys,wrt32x) ubootenv_add_uci_config "/dev/mtd1" "0x0" "0x20000" "0x20000" ;;
So those scripts simply generate /etc/fw_env.config required by fw_printenv / fw_setenv. They have to match what's used by U-Boot at compilation time.
My long term plan is to move that info to DTS and share it across projects.