[PATCH v6 6/7] doc: Improve environment documentation

Simon Glass sjg at chromium.org
Thu Oct 14 20:22:56 CEST 2021

Make various updates suggested during review of the rST conversion.

Signed-off-by: Simon Glass <sjg at chromium.org>
Suggested-by: Wolfgang Denk <wd at denx.de>

Changes in v6:
- Move all updates to a separate patch
- More updates and improvements

Changes in v5:
- Minor updates as suggested by Wolfgang

Changes in v4:
- Add new patch to move environment documentation to rST

 doc/usage/environment.rst | 35 ++++++++++++++++++++++++++---------
 doc/usage/index.rst       |  1 +
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
index 76915484b85..ef9cd20715a 100644
--- a/doc/usage/environment.rst
+++ b/doc/usage/environment.rst
@@ -5,16 +5,20 @@ Environment Variables
 U-Boot supports user configuration using Environment Variables which
-can be made persistent by saving to Flash memory.
+can be made persistent by saving to persistent storage, for example flash
-Environment Variables are set using "setenv", printed using
-"printenv", and saved to Flash using "saveenv". Using "setenv"
+Environment Variables are set using "env set" (alias "setenv"), printed using
+"env print" (alias "printenv"), and saved to persistent storage using
+"env save" (alias "saveenv"). Using "env set"
 without a value can be used to delete a variable from the
 environment. As long as you don't save the environment you are
 working with an in-memory copy. In case the Flash area containing the
 environment is erased by accident, a default environment is provided.
-Some configuration options can be set using Environment Variables.
+Some configuration is controlled by Environment Variables, so that setting the
+variable can adjust the behaviour of U-Boot (e.g. autoboot delay, autoloading
+from tftp).
 The default environment is created in `include/env_default.h`, and can be
 augmented by various `CONFIG` defines. See that file for details. In
@@ -68,18 +72,25 @@ Example::
         echo CONFIG_SYS_BOARD boot failed - please check your image
         echo Load address is CONFIG_SYS_LOAD_ADDR
-Some configuration options can be set using Environment Variables.
+Some configuration options can be set using Environment Variables. In many cases
+the value in the default environment comes from a CONFIG option - see
+`include/env_default.h`) for this.
 List of environment variables (most likely not complete):
+    Current baud rate used by the serial console. The built-in value is set by
+    CONFIG_BAUDRATE (see `drivers/serial/Kconfig`)
+    Current autoboot delay. The built-in value is set by CONFIG_BOOTDELAY (see
+    `common/Kconfig`)
+    Defines a command string that is automatically executed when no character
+    is read on the console interface within a cetain boot delay after reset.
+    The built-in value is set by CONFIG_BOOTCOMMAND (see `common/Kconfig`)
     Boot arguments when booting an RTOS image
@@ -125,7 +136,7 @@ autoload
     if set to "no" (any string beginning with 'n'),
     "bootp" will just load perform a lookup of the
     configuration from the BOOTP server, but not try to
-    load any image using TFTP
+    load any image using TFTP or DHCP.
     if set to "yes", an image loaded using the "bootp",
@@ -291,6 +302,8 @@ vlan
     Ethernet is encapsulated/received over 802.1q
     VLAN tagged frames.
+    Note: This appears not to be used in U-Boot. See `README.VLAN`.
     Period during which BOOTP/DHCP sends retries.
     Unsigned value, in milliseconds. If not set, the period will
@@ -332,6 +345,10 @@ flash or offset in NAND flash.
 boards currently use other variables for these purposes, and some
 boards use these variables for other purposes.
+Also note that most of these variables are just a commonly used set of variable
+names, used in some other variable definitions, but are not hard-coded anywhere
+in U-Boot code.
 ================= ============== ================ ==============
 Image             File Name      RAM Address      Flash Location
 ================= ============== ================ ==============
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 356f2a56181..1a79d1c03eb 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -5,6 +5,7 @@ Use U-Boot
    :maxdepth: 1
+   environment

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