[PATCH v7 6/7] doc: Improve environment documentation

Simon Glass
2021-10-16T00:35:16Z

Make various updates suggested during review of the rST conversion.

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

Changes in v7:
- A few more tweaks

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 | 36 +++++++++++++++++++++++++++---------
doc/usage/index.rst | 1 +
2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
index a2410607e9f..c4fd07aa939 100644
--- a/doc/usage/environment.rst
+++ b/doc/usage/environment.rst
@@ -4,16 +4,20 @@ 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
+memory.

-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
+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).

Text-based Environment
----------------------
@@ -90,16 +94,24 @@ environment but work is underway to address this.
List of 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.
+
This is most-likely not complete:

baudrate
- see CONFIG_BAUDRATE
+ Current baud rate used by the serial console. The built-in value is set by
+ CONFIG_BAUDRATE (see `drivers/serial/Kconfig`)

bootdelay
- see CONFIG_BOOTDELAY
+ Current autoboot delay. The built-in value is set by CONFIG_BOOTDELAY (see
+ `common/Kconfig`)

bootcmd
- see CONFIG_BOOTCOMMAND
+ 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`)

bootargs
Boot arguments when booting an RTOS image
@@ -145,7 +157,7 @@ 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.

autostart
if set to "yes", an image loaded using the "bootp",
@@ -311,6 +323,8 @@ vlan
Ethernet is encapsulated/received over 802.1q
VLAN tagged frames.

+ Note: This appears not to be used in U-Boot. See `README.VLAN`.
+
bootpretryperiod
Period during which BOOTP/DHCP sends retries.
Unsigned value, in milliseconds. If not set, the period will
@@ -352,6 +366,10 @@ 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

dfu
+ environment
fdt_overlays
fit
netconsole
--
2.33.0.1079.g6e70778dc9-goog