diff --git a/sys/dev/ichwd/ichwd.c b/sys/dev/ichwd/ichwd.c
index 71662a5..a4387a2 100644
--- a/sys/dev/ichwd/ichwd.c
+++ b/sys/dev/ichwd/ichwd.c
@@ -62,6 +62,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/kernel.h>
 #include <sys/module.h>
 #include <sys/systm.h>
+#include <sys/sysctl.h>
 #include <sys/bus.h>
 #include <machine/bus.h>
 #include <sys/rman.h>
@@ -72,6 +73,14 @@ __FBSDID("$FreeBSD$");
 
 #include <dev/ichwd/ichwd.h>
 
+
+static int use_global_smi = 0;
+
+SYSCTL_NODE(_hw, OID_AUTO, ichwd, CTLFLAG_RD, 0, "ichwd driver global parameters");
+TUNABLE_INT("hw.ichwd.use_global_smi", &use_global_smi);
+SYSCTL_INT(_hw_ichwd, OID_AUTO, use_global_smi, CTLFLAG_RDTUN, &use_global_smi, 0,
+	   "ichwd may try to change global SMI Enable bit if TCO SMI bit is locked");
+
 static struct ichwd_device ichwd_devices[] = {
 	{ DEVICEID_82801AA,  "Intel 82801AA watchdog timer",	1 },
 	{ DEVICEID_82801AB,  "Intel 82801AB watchdog timer",	1 },
@@ -152,7 +161,37 @@ static devclass_t ichwd_devclass;
 static __inline void
 ichwd_smi_disable(struct ichwd_softc *sc)
 {
-	ichwd_write_smi_4(sc, SMI_EN, ichwd_read_smi_4(sc, SMI_EN) & ~SMI_TCO_EN);
+	uint32_t val;
+
+	val = ichwd_read_smi_4(sc, SMI_EN);
+
+	/* check if either TCO SMI is disabled or SMI is disabled globally */
+	if ((val & (SMI_TCO_EN | SMI_GBL_EN)) != (SMI_TCO_EN | SMI_GBL_EN))
+		return;
+	/* first try to disabled TCO SMI */
+	val &= ~SMI_TCO_EN;
+	ichwd_write_smi_4(sc, SMI_EN, val);
+
+	/* check if TCO SMI got disabled */
+	val = ichwd_read_smi_4(sc, SMI_EN);
+	if ((val & SMI_TCO_EN) == 0)
+		return;
+	printf("could not disable TCO SMI, bit might be locked by BIOS\n");
+
+	/* check if user allowed to fiddle with global SMI settings */
+	if (!use_global_smi)
+		return;
+
+	/* try to disable SMI globally */
+	val &= ~SMI_GBL_EN;
+	ichwd_write_smi_4(sc, SMI_EN, val);
+
+	/* check results */
+	val = ichwd_read_smi_4(sc, SMI_EN);
+	if (val & SMI_GBL_EN)
+		printf("could not disable SMI globally, bit might be locked by BIOS\n");
+	else
+		printf("disabled SMI globally (permitted by use_global_smi tunable)\n");
 }
 
 /*
@@ -161,7 +200,30 @@ ichwd_smi_disable(struct ichwd_softc *sc)
 static __inline void
 ichwd_smi_enable(struct ichwd_softc *sc)
 {
-	ichwd_write_smi_4(sc, SMI_EN, ichwd_read_smi_4(sc, SMI_EN) | SMI_TCO_EN);
+	uint32_t val;
+
+	val = ichwd_read_smi_4(sc, SMI_EN);
+
+	/* check if both TCO SMI and global SMI are already enabled */
+	if ((val & (SMI_TCO_EN | SMI_GBL_EN)) == (SMI_TCO_EN | SMI_GBL_EN))
+		return;
+
+	/* try to enable TCO SMI and global SMI if permitted */
+	val |= SMI_TCO_EN;
+	if (use_global_smi)
+		val |= SMI_GBL_EN;
+
+	/* bail out if SMI is globally disabled and user doesn't allow to change that */
+	if ((val & SMI_GBL_EN) == 0) {
+		printf("could not enable TCO SMI because SMI is globally disabled\n");
+		return;
+	}
+	ichwd_write_smi_4(sc, SMI_EN, val);
+
+	/* check if we succeeded */
+	val = ichwd_read_smi_4(sc, SMI_EN);
+	if ((val & (SMI_TCO_EN | SMI_GBL_EN)) != (SMI_TCO_EN | SMI_GBL_EN))
+		printf("could not enable SMIs, bits might be locked by BIOS\n");
 }
 
 /*
diff --git a/sys/dev/ichwd/ichwd.h b/sys/dev/ichwd/ichwd.h
index 51ed26d..8e2bdba 100644
--- a/sys/dev/ichwd/ichwd.h
+++ b/sys/dev/ichwd/ichwd.h
@@ -131,9 +131,9 @@ struct ichwd_softc {
 #define TCO1_CNT		0x08 /* TCO Control 1 */
 #define TCO2_CNT		0x08 /* TCO Control 2 */
 
-/* bit definitions for SMI_EN and SMI_STS */
+/* SMI-related bit definitions */
+#define SMI_GBL_EN		0x0001
 #define SMI_TCO_EN		0x2000
-#define SMI_TCO_STS		0x2000
 
 /* timer value mask for TCO_RLD and TCO_TMR */
 #define TCO_TIMER_MASK		0x1f