sandbox: add SIGALRM-based watchdog device

In order to test that U-Boot actually maintains the watchdog device(s)
during long-running busy-loops, such as those where we wait for the
user to stop autoboot, we need a watchdog device that actually does
something during those loops; we cannot test that behaviour via the DM
test framework.

So introduce a relatively simple watchdog device which is simply based
on calling the host OS' alarm() function; that has the nice property
that a new call to alarm() simply sets a new deadline, and alarm(0)
cancels any existing alarm. These properties are precisely what we
need to implement start/reset/stop. We install our own handler so that
we get a known message printed if and when the watchdog fires, and by
just invoking that handler directly, we get expire_now for free.

The actual calls to the various OS functions (alarm, signal, raise)
need to be done in os.c, and since the driver code cannot get access
to the values of SIGALRM or SIG_DFL (that would require including a
host header, and that's only os.c which can do that), we cannot simply
do trivial wrappers for signal() and raise(), but instead create
specialized functions just for use by this driver.

Apart from enabling this driver for sandbox{,64}_defconfig, also
enable the wdt command which was useful for hand-testing this new
driver (especially with running u-boot under strace).

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/os.h b/include/os.h
index 5b353ae9d9..54874f5e0e 100644
--- a/include/os.h
+++ b/include/os.h
@@ -109,6 +109,23 @@ int os_unlink(const char *pathname);
 void os_exit(int exit_code) __attribute__((noreturn));
 
 /**
+ * os_alarm() - access to the OS alarm() system call
+ */
+unsigned int os_alarm(unsigned int seconds);
+
+/**
+ * os_set_alarm_handler() - set handler for SIGALRM
+ *
+ * @handler:   The handler function. Pass NULL for SIG_DFL.
+ */
+void os_set_alarm_handler(void (*handler)(int));
+
+/**
+ * os_raise_sigalrm() - do raise(SIGALRM)
+ */
+void os_raise_sigalrm(void);
+
+/**
  * os_tty_raw() - put tty into raw mode to mimic serial console better
  *
  * @fd:		File descriptor of stdin (normally 0)