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>

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
 

drivers/bootcount/Makefile

@@ -8,3 +8,4 @@ obj-$(CONFIG_BLACKFIN)		+= bootcount_blackfin.o
 obj-$(CONFIG_SOC_DA8XX)		+= bootcount_davinci.o
 obj-$(CONFIG_AM33XX)		+= bootcount_davinci.o
 obj-$(CONFIG_BOOTCOUNT_RAM)	+= bootcount_ram.o
+obj-$(CONFIG_BOOTCOUNT_ENV)	+= bootcount_env.o

drivers/bootcount/bootcount_env.c

@@ -0,0 +1,29 @@
+/*
+ * (C) Copyright 2013
+ * Heiko Schocher, DENX Software Engineering, hs@denx.de.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+
+void bootcount_store(ulong a)
+{
+	int upgrade_available = getenv_ulong("upgrade_available", 10, 0);
+
+	if (upgrade_available) {
+		setenv_ulong("bootcount", a);
+		saveenv();
+	}
+}
+
+ulong bootcount_load(void)
+{
+	int upgrade_available = getenv_ulong("upgrade_available", 10, 0);
+	ulong val = 0;
+
+	if (upgrade_available)
+		val = getenv_ulong("bootcount", 10, 0);
+
+	return val;
+}