bootcount: store bootcount var in environment

If no softreset save registers are found on the hardware
"bootcount" is stored in the environment. To prevent a
saveenv on all reboots, the environment variable
"upgrade_available" is introduced. If "upgrade_available" is
0, "bootcount" is always 0 therefore no need to save the
environment on u-boot boot, if "upgrade_available" is 1 "bootcount"
is incremented in the environment and environment gets written
on u-boot start.
So the Userspace Applikation must set the "upgrade_available"
and "bootcount" variable to 0 (for example with fw_setenv),
if a boot was successfully.

Signed-off-by: Heiko Schocher <hs@denx.de>

1 files changed, 16 insertions, 0 deletions

diff --git a/README b/README
index a70475f..39b3fe6 100644
--- a/README
+++ b/README
@@ -784,6 +784,22 @@ The following options need to be configured:
 		as a convenience, when switching between booting from
 		RAM and NFS.
 
+- Bootcount:
+		CONFIG_BOOTCOUNT_LIMIT
+		Implements a mechanism for detecting a repeating reboot
+		cycle, see:
+		http://www.denx.de/wiki/view/DULG/UBootBootCountLimit
+
+		CONFIG_BOOTCOUNT_ENV
+		If no softreset save registers are found on the hardware
+		"bootcount" is stored in the environment. To prevent a
+		saveenv on all reboots, the environment variable
+		"upgrade_available" is used. If "upgrade_available" is
+		0, "bootcount" is always 0, if "upgrade_available" is
+		1 "bootcount" is incremented in the environment.
+		So the Userspace Applikation must set the "upgrade_available"
+		and "bootcount" variable to 0, if a boot was successfully.
+
 - Pre-Boot Commands:
 		CONFIG_PREBOOT