Add locking to the hardware drivers. I intended to figure out more

precisely where locking would be needed before adding it, but it
seems uart(4) draws slightly too much attention to have it without
locking for too long.
The lock added is a spinlock that protects access to the underlying
hardware. As a first and obvious stab at this, each method of the
hardware interface grabs the lock. Roughly speaking this serializes
the methods. Exceptions are the probe, attach and detach methods.

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/dev/uart/uart_bus.h b/sys/dev/uart/uart_bus.h
index bd0bab7..dde9ff8 100644
--- a/sys/dev/uart/uart_bus.h
+++ b/sys/dev/uart/uart_bus.h
@@ -113,6 +113,8 @@ struct uart_softc {
 	struct uart_bas	sc_bas;
 	device_t	sc_dev;
 
+	struct mtx	sc_hwmtx;	/* Spinlock protecting hardware. */
+
 	struct resource	*sc_rres;	/* Register resource. */
 	int		sc_rrid;
 	int		sc_rtype;	/* SYS_RES_{IOPORT|MEMORY}. */