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[RFC,00/10] env: Multiple env support and env transition for sunxi

Message ID 20171116092231.27740-1-maxime.ripard@free-electrons.com
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Series env: Multiple env support and env transition for sunxi | expand

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Maxime Ripard Nov. 16, 2017, 9:22 a.m. UTC 
Hi,

Here is a second attempt at transitioning away from the MMC raw
environment to a FAT-based one.

You'll find the first one here for reference:
https://lists.denx.de/pipermail/u-boot/2017-October/310111.html

The fundamental issue I'm trying to adress is that we've had for a
very long time the assumption that the main U-Boot binary wouldn't
exceed around 500 bytes.

However, we're starting to get real close to that limit, and are
running out of silver bullets to deal with the consequences of having
a bigger U-Boot binary, the main consequence being that we would
have some overlap between the environment and U-Boot.

One way to address this that has been suggested by Tom is to move away
from the raw MMC environment to a FAT-based one. This would allow us
to slowly migrate away, and eventually remove the MMC-raw option
entirely to reclaim that space for the binary.

That cannot be done in a single release however, since we might have
environments in the wild already that people rely on. And since we
always encouraged people to use the raw MMC environment, noone would
expect that.

This is even worse since some platforms are using the U-Boot
environment to deal with implement their upgrade mechanism, such as
mender.io, and force moving the environment would break any further
upgrade.

The suggested implementation is to allow U-Boot to compile multiple
environments backend at once, based on the work done by Simon. The
default behaviour shouldn't change obviously. We can then piggy-back
on this to tweak on a per-board basis the environment lookup algorithm
to always favour the FAT-based environment and then fallback to the
MMC. It will allow us to migrate a raw-MMC user to a FAT based
solution as soon as they update their environment (assuming that there
is a bootable FAT partition in the system).

This has just been compile tested on sunxi so far, and I'd like
general comments on the approach taken. Obviously, this will need to
work properly before being merged.

Let me know what you think,
Maxime

Maxime Ripard (10):
  cmd: nvedit: Get rid of the env lookup
  env: Make env_driver_lookup_default private
  env: Rename env_driver_lookup_default and env_get_default_location
  env: Pass additional parameters to the env lookup function
  env: Make the env save message a bit more explicit
  env: Support multiple environments
  env: Allow to build multiple environments in Kconfig
  env: Mark env_get_location as weak
  sunxi: Transition from the MMC to a FAT-based environment
  env: sunxi: Enable FAT-based environment support by default

 board/sunxi/board.c   |  16 +++++
 cmd/nvedit.c          |   4 --
 env/Kconfig           |  69 +++++++++---------
 env/env.c             | 194 ++++++++++++++++++++++++++++++++------------------
 include/environment.h |  14 ++--
 5 files changed, 182 insertions(+), 115 deletions(-)