Messages in this thread | | | Date | Mon, 7 Mar 2022 11:31:23 +0100 | Subject | Re: [PATCH V2] dt-bindings: nvmem: add U-Boot environment variables binding | From | Rafał Miłecki <> |
| |
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-envtools/files;h=687c89806f72756053457a7ab7245bff1c4dcfe8;hb=HEAD
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.
| |