panic: Provide a way to poweroff on panic

For sandbox it normally doesn't make sense to reset when a panic occurs,
since presumably it will just happen again. Add an option to power off
instead.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <sjg@chromium.org>

lib/Kconfig

@@ -263,6 +263,14 @@ config PANIC_HANG
 	  development since you can try to debug the conditions that lead to
 	  the situation.
 
+config PANIC_POWEROFF
+	bool "Power off the system on fatal error"
+	help
+	  Define this option to power off the system in case of a fatal error,
+	  instead of resetting. This is useful for development and testing to
+	  avoid infinite reset loops when debugging issues like stack smashing.
+	  The system will power off using sysreset.
+
 config REGEX
 	bool "Enable regular expression support"
 	default y if NET

lib/panic.c

@@ -13,6 +13,9 @@
 #if !defined(CONFIG_PANIC_HANG)
 #include <command.h>
 #endif
+#if defined(CONFIG_PANIC_POWEROFF)
+#include <sysreset.h>
+#endif
 #include <linux/delay.h>
 #include <stdio.h>
 
@@ -23,6 +26,11 @@ static void panic_finish(void)
 	putc('\n');
 #if defined(CONFIG_PANIC_HANG)
 	hang();
+#elif defined(CONFIG_PANIC_POWEROFF)
+	flush();  /* flush the panic message before power off */
+
+	sysreset_walk(SYSRESET_POWER_OFF);
+	hang();  /* hang if power off fails */
 #else
 	flush();  /* flush the panic message before reset */