[PATCH 0/5] Board specific runtime determined default env

Marek Behún kabel at kernel.org
Thu Oct 28 05:28:05 CEST 2021

From: Marek Behún <marek.behun at nic.cz>

Hello Simon, Stefan, Pali,

this series adds support for board specific runtime determined
default environment variables.

IMPORTANT: This series depends on the series

Currently the
  env default [-a]
command uses the default_environment[] buffer to get the default
env variables.

Sometimes it makes sense to have runtime determined default env

For example the ESPRESSObin board has 4 variants
([ddr3 vs ddr4] x [emmc vs sd]), and each uses different device tree.
Thus the `fdtfile` env variable has different values for these 4
variants. (We can't set this variable via env_set() in some board init
function, because then the user would be unable to overwrite it.)
In order for the command
  env default fdtfile
to work as the user would expect, we need to support overwriting default
environment in runtime.

Pali solved this for ESPRESSObin by declaring the default_environment[]
buffer read-write, instead of read-only, and adding ad-hoc code into
board_late_init() that writes into the default_environment[] buffer.

This ad-hoc code works, but it would be better to have a generic API
for this, since there are other boards which could benefit.

The first 3 patches in this series fix and simplify code in

The 4th patch adds support for board specific runtime determined
default environment in such a way that if a board code defines function

  const char *board_special_default_env(unsigned i, const char **name);

The default weak implementation of this function is trivial and just
returns NULL.
This function is to be defined in board code, and when defined, it must
return the value of the i-th runtime determined default env variable,
while storing its name into *name.

For example:
  const char *board_special_default_env(unsigned i, const char **name)
    switch (i) {
    case 0:
      *name = "board";
      return is_ddr4() ? "my_board_ddr4" : "my_board";
    case 1:
      *name = "fdtfile";
      return is_ddr4() ? "my-board-ddr4.dtb" : "my-board.dtb";
      return NULL;

The last patch (NOT TESTED) converts the ESPRESSObin ad-hoc code to
use this API.


Marek Behún (5):
  env: Don't set ready flag if import failed in env_set_default()
  env: Fix env_get() when returning empty string using env_get_f()
  env: Simplify env_get_default()
  env: Add support for board specific special default environment
  arm: mvebu: Espressobin: Use new API for setting default env at

 board/Marvell/mvebu_armada-37xx/board.c     | 120 ++++++++++------
 configs/mvebu_espressobin-88f3720_defconfig |   1 -
 env/common.c                                | 150 ++++++++++++++++----
 include/configs/mvebu_armada-37xx.h         |  17 +--
 include/env_default.h                       |   2 -
 include/env_internal.h                      |   4 -
 6 files changed, 199 insertions(+), 95 deletions(-)


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