Hi Stefano,
On 2 May 2018 at 02:48, Stefano Babic sbabic@denx.de wrote:
Hi,
I am thinking about how it is possible to export in a clean way the default environment from u-boot. The general use case happens when the environment must be changed from user space (via fw_setenv or whatever) and no environment was still stored - board boots with default environment.
Up now, the trick is to compile the environment tools (u-boot-fw-utils in Yocto) with exactly the same U-Boot sources. This works, but it is error prone when a new Yocto version is delivered (and maybe with a different u-boot-fw-utils) or even if the bootloader is updated. I am searching for an alterntive method.
The code in tools/env is really generic, but it becomes board specific just for the default environment. If the default environment can read in a reliable way from u-boot itslef (its binary), the tool can search for the default environment instead of linking again, and tools/env becomes "distro capable" - one binary that works on all boards.
I have some thoughts and I would like to share, maybe some of you has better ideas. So what I would like to get directly from the binary is the offset of "default_environment" (default_environment) CONFIG_SYS_TEXT_BASE:
- put this offset in the .img header. Yes, it works just for SPL /
u-boot.img (drawback).
How about putting the default environment in a FIT? That is typically easy to find using the magic word.
- surround default environment with some easy to recognize magic number.
Offset is not known, but user space can find it, like
magic (long string) ... default_environment end default environment (long string)
Seems like FIT would take care of this for you.
- adding a section in the linker. I think we tried something in the
past, see __UBOOT_ENV_SECTION__ (it replaced __PPCENV__ from the old good mpc8xx times..) that is currently unused. I do not like this approach, it can increase (due to alignment) footprint in SPL, where I am starting to have issues for smaller i.MX.
Also I wonder if compression might be useful? FIT supports that fairly easily.
- export the deafult environment with such a tool. This dump can be
passed as input to the program in user space. Well, it could be done, but I still suffer if something is changed (sync is required to have always the correct dump, I do not see improvement here).
Any thought ?
Regards, Simon