On 1/31/20 7:54 AM, Tom Rini wrote:
On Fri, Jan 31, 2020 at 02:42:25PM +0000, Jon Hunter wrote:
On 31/01/2020 14:05, Tom Rini wrote:
On Fri, Jan 31, 2020 at 01:24:21PM +0000, Jon Hunter wrote:
On 31/01/2020 12:42, Soeren Moch wrote:
On 31.01.20 11:59, Jon Hunter wrote:
U-Boot supports loading a user environment from a file in the
file-system. Therefore to make it easier for users to override the
default environment, add support to the 'distro_bootcmd' to look for
and load a user environment in a file called 'uEnv.txt' in the same
locations where an extlinux.conf or boot script might be found.
We already have boot script support, which can easily be used to modify
the environment. Do we really need to bloat the distro_boot machinery
further with environment import, that is quite limited in contrast to
boot scripts?
If you are booting with an extlinux.conf file, as we do by default, then
if this file is found, this is always booted from before you have the
opportunity to run the boot.scr script.
Furthermore if you did switch the order to boot from a boot.scr script
before the extlinux.conf, but you just wanted to do some simple
modifications of the environment before booting (ie. so the boot.scr
does not actually boot the system), then as the code is today you get a
'echo SCRIPT FAILED: continuing...' message.
Yes this could be changed, but just seems cleaner and simpler to add
support to make changes to the environment before the extlinux.conf is
loaded.
Yes this does add more to the environment, but it is hardly significant
bloat, but if that is a concern then we could always disable this by
default and allow users to enable it.
This is something I think we had talked about and rejected doing
initially. Can you please expand on the use-case here, and why it's
perhaps not better handled via PREBOOT on some platforms? Thanks!
We have one specific use-case in a downstream version of u-boot where we
store some parameters in the u-boot environment for tweaking the DT
firmware on boot [0]. Now there are cases where we do not wish to modify
DT at all and so want to clear these variables and I would like a way to
automate the re-configuration of the u-boot environment without the user
having to manually set these just by the presence of a uEnv.txt file on
the disk.
Admittedly, this particular use-case/scenario is not directly applicable
to the mainline u-boot branch as there is no support for these
environment variables for Tegra (yet). However, it seemed that this
change would have some value in upstream u-boot as well to allow the
user to change any default environment variables without having to
re-compile and hence, I decided submit this change here.
For example, if we wanted to tweak any of the default environment
variables that are currently in 'include/configs/tegra210-common.h' we
could. Now you may say if we are not tweaking these very often, then why
not recompile, and we could, but given that we have the ability to load
environment parameters from a file on disk, it seems as shame that in
the current boot flow there is no way to make use of this extremely
useful feature.
I really think this is a good case for CONFIG_PREBOOT to execute a
script (and we have other examples of that today) rather than something
to put in to distro boot for everyone. Thanks!
I can definitely imagine there are many reasons a user might want to
have a way to modify U-Boot's environment easily via creating/editing
uEnv.txt rather than having to interactively run setenv/saveenv on the
U-Boot console.
So, I think the main question is where to place uEnv.txt. If we use
CONFIG_PREBOOT, we'd either have to:
a) Hard-code a single storage device to load it from, which involved
deciding on a platform-by-platform basis which is the best location to
load it from.
OR:
b) Duplicate the existing device scanning logic from the distro boot
scripts into CONFIG_PREBOOT. I'd rather not see the duplication.
This patch achieves the auto-scanning for uEnv.txt without the
disadvantage of (b) above. Also, it allows uEnv.txt to follow a
removable storage device, which can have advantages. In the specific
use-case Jon is working on, we'll want to edit the environment to
disable some U-Boot features when using an upstream kernel, and not do
that editing when booting a downstream kernel. On the particular
platform Jon is using, the primary storage device is an SD card. If
uEnv.txt can follow the SD card that'd be very useful. Of course, we
could just hard-code the SD card as the location of uEnv.txt, but that
wouldn't work well for systems that don't use removable media as the
primary storage location (so we'd choose to look for uEnv.txt on e.g.
fixed eMMC) yet the user has actually chosen to boot from SD card (which
is earlier in boot_targets to allow booting from SD).
In summary, I think doing this in the distro boot commands probably does
make sense.
