o mc146818(4):

- Add locking.
  - Account for if the MC146818_NO_CENT_ADJUST flag is set we don't need
    to check wheter year < POSIX_BASE_YEAR.
  - Add some comments about mapping the day of week from the range the
    generic clock code uses to the range the chip uses and which I meant
    to add in the initial version.
  - Minor clean-up, use __func__ instead of hardcoded function names in
    error strings.

o in the rtc(4) front-end additionally:
  - Don't leak resources in case mc146818_attach() fails.
  - Account for ebus(4) defaulting to SYS_RES_MEMORY for the memory
    resources since ebus.c rev. 1.22.

sys/dev/mc146818/mc146818.c

@@ -37,6 +37,8 @@ __FBSDID("$FreeBSD$");
 #include <sys/systm.h>
 #include <sys/bus.h>
 #include <sys/clock.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
 
 #include <machine/bus.h>
 
@@ -57,6 +59,11 @@ mc146818_attach(device_t dev)
 
 	sc = device_get_softc(dev);
 
+	if (mtx_initialized(&sc->sc_mtx) == 0) {
+		device_printf(dev, "%s: mutex not initialized\n", __func__);
+		return (ENXIO);
+	}
+
 	if (sc->sc_mcread == NULL)
 		sc->sc_mcread = mc146818_def_read;
 	if (sc->sc_mcwrite == NULL)
@@ -73,8 +80,10 @@ mc146818_attach(device_t dev)
 			sc->sc_setcent = mc146818_def_setcent;
 	}
 
+	mtx_lock(&sc->sc_mtx);
 	if (!(*sc->sc_mcread)(dev, MC_REGD) & MC_REGD_VRT) {
-		device_printf(dev, "mc146818_attach: battery low\n");
+		mtx_unlock(&sc->sc_mtx);
+		device_printf(dev, "%s: battery low\n", __func__);
 		return (ENXIO);
 	}
 
@@ -85,6 +94,7 @@ mc146818_attach(device_t dev)
 	sc->sc_regb |= (sc->sc_flag & MC146818_BCD) ? 0 : MC_REGB_BINARY;
 	sc->sc_regb |= (sc->sc_flag & MC146818_12HR) ? 0 : MC_REGB_24HR;
 	(*sc->sc_mcwrite)(dev, MC_REGB, sc->sc_regb);
+	mtx_unlock(&sc->sc_mtx);
 
 	clock_register(dev, 1000000);	/* 1 second resolution. */
 
@@ -106,12 +116,7 @@ mc146818_gettime(device_t dev, struct timespec *ts)
 
 	timeout = 1000000;	/* XXX how long should we wait? */
 
-	/*
-	 * XXX:	Use a spinlock to mutex register access and increase the
-	 *	likelihood that all registers are read before an update
-	 *	occurs.
-	 */
-
+	mtx_lock(&sc->sc_mtx);
 	/*
 	 * If MC_REGA_UIP is 0 we have at least 244us before the next
 	 * update. If it's 1 an update is imminent.
@@ -120,7 +125,8 @@ mc146818_gettime(device_t dev, struct timespec *ts)
 		if (!((*sc->sc_mcread)(dev, MC_REGA) & MC_REGA_UIP))
 			break;
 		if (--timeout < 0) {
-			device_printf(dev, "mc146818_gettime: timeout\n");
+			mtx_unlock(&sc->sc_mtx);
+			device_printf(dev, "%s: timeout\n", __func__);
 			return (EBUSY);
 		}
 	}
@@ -131,18 +137,19 @@ mc146818_gettime(device_t dev, struct timespec *ts)
 	ct.sec = FROMREG((*sc->sc_mcread)(dev, MC_SEC));
 	ct.min = FROMREG((*sc->sc_mcread)(dev, MC_MIN));
 	ct.hour = FROMREG((*sc->sc_mcread)(dev, MC_HOUR));
+	/* Map dow from 1 - 7 to 0 - 6. */
 	ct.dow = FROMREG((*sc->sc_mcread)(dev, MC_DOW)) - 1;
 	ct.day = FROMREG((*sc->sc_mcread)(dev, MC_DOM));
 	ct.mon = FROMREG((*sc->sc_mcread)(dev, MC_MONTH));
 	year = FROMREG((*sc->sc_mcread)(dev, MC_YEAR));
-	if (sc->sc_getcent) {
+	year += sc->sc_year0;
+	if (sc->sc_flag & MC146818_NO_CENT_ADJUST) {
 		cent = (*sc->sc_getcent)(dev);
 		year += cent * 100;
-	}
-
-	year += sc->sc_year0;
-	if (year < POSIX_BASE_YEAR && !(sc->sc_flag & MC146818_NO_CENT_ADJUST))
+	} else if (year < POSIX_BASE_YEAR)
 		year += 100;
+	mtx_unlock(&sc->sc_mtx);
+
 	ct.year = year;
 
 	return (clock_ct_to_ts(&ct, ts));
@@ -159,16 +166,19 @@ mc146818_getsecs(device_t dev, int *secp)
 
 	timeout = 1000000;	/* XXX how long should we wait? */
 
+	mtx_lock(&sc->sc_mtx);
 	for (;;) {
 		if (!((*sc->sc_mcread)(dev, MC_REGA) & MC_REGA_UIP)) {
 			sec = FROMREG((*sc->sc_mcread)(dev, MC_SEC));
 			break;
 		}
 		if (--timeout == 0) {
-			device_printf(dev, "mc146818_getsecs: timeout\n");
+			mtx_unlock(&sc->sc_mtx);
+			device_printf(dev, "%s: timeout\n", __func__);
 			return (EBUSY);
 		}
 	}
+	mtx_unlock(&sc->sc_mtx);
 
 #undef FROMREG
 
@@ -196,6 +206,7 @@ mc146818_settime(device_t dev, struct timespec *ts)
 	ts->tv_nsec = 0;
 	clock_ts_to_ct(ts, &ct);
 
+	mtx_lock(&sc->sc_mtx);
 	/* Disable RTC updates and interrupts (if enabled). */
 	(*sc->sc_mcwrite)(dev, MC_REGB,
 	    ((sc->sc_regb & (MC_REGB_BINARY | MC_REGB_24HR)) | MC_REGB_SET));
@@ -205,22 +216,23 @@ mc146818_settime(device_t dev, struct timespec *ts)
 	(*sc->sc_mcwrite)(dev, MC_SEC, TOREG(ct.sec));
 	(*sc->sc_mcwrite)(dev, MC_MIN, TOREG(ct.min));
 	(*sc->sc_mcwrite)(dev, MC_HOUR, TOREG(ct.hour));
+	/* Map dow from 0 - 6 to 1 - 7. */
 	(*sc->sc_mcwrite)(dev, MC_DOW, TOREG(ct.dow + 1));
 	(*sc->sc_mcwrite)(dev, MC_DOM, TOREG(ct.day));
 	(*sc->sc_mcwrite)(dev, MC_MONTH, TOREG(ct.mon));
 
 	year = ct.year - sc->sc_year0;
-	if (sc->sc_setcent) {
+	if (sc->sc_flag & MC146818_NO_CENT_ADJUST) {
 		cent = year / 100;
 		(*sc->sc_setcent)(dev, cent);
 		year -= cent * 100;
-	}
-	if (year > 99 && (sc->sc_flag & MC146818_NO_CENT_ADJUST) == 0)
+	} else if (year > 99)
 		year -= 100;
 	(*sc->sc_mcwrite)(dev, MC_YEAR, TOREG(year));
 
 	/* Reenable RTC updates and interrupts. */
 	(*sc->sc_mcwrite)(dev, MC_REGB, sc->sc_regb);
+	mtx_unlock(&sc->sc_mtx);
 
 #undef TOREG
 

sys/dev/mc146818/mc146818var.h

@@ -32,6 +32,8 @@ struct mc146818_softc {
 	bus_space_tag_t	sc_bst;			/* bus space tag */
 	bus_space_handle_t sc_bsh;		/* bus space handle */
 
+	struct mtx sc_mtx;			/* hardware mutex */
+
 	u_char sc_rega;				/* register A */
 	u_char sc_regb;				/* register B */
 

sys/sparc64/sparc64/rtc.c

@@ -39,7 +39,9 @@ __FBSDID("$FreeBSD$");
 #include <sys/systm.h>
 #include <sys/bus.h>
 #include <sys/kernel.h>
+#include <sys/lock.h>
 #include <sys/module.h>
+#include <sys/mutex.h>
 #include <sys/resource.h>
 
 #include <dev/ofw/ofw_bus.h>
@@ -71,9 +73,6 @@ static device_method_t rtc_ebus_methods[] = {
 	/* clock interface */
 	DEVMETHOD(clock_gettime,	mc146818_gettime),
 	DEVMETHOD(clock_settime,	mc146818_settime),
-#ifdef notyet
-	DEVMETHOD(clock_getsecs,	mc146818_getsecs),
-#endif
 
 	{ 0, 0 }
 };
@@ -95,9 +94,6 @@ static device_method_t rtc_isa_methods[] = {
 	/* clock interface */
 	DEVMETHOD(clock_gettime,	mc146818_gettime),
 	DEVMETHOD(clock_settime,	mc146818_settime),
-#ifdef notyet
-	DEVMETHOD(clock_getsecs,	mc146818_getsecs),
-#endif
 
 	{ 0, 0 }
 };
@@ -148,16 +144,24 @@ rtc_attach(device_t dev)
 	struct timespec ts;
 	struct mc146818_softc *sc;
 	struct resource *res;
-	int error, rid;
+	int error, rid, rtype;
 
 	sc = device_get_softc(dev);
 	bzero(sc, sizeof(struct mc146818_softc));
 
+	mtx_init(&sc->sc_mtx, "rtc_mtx", NULL, MTX_DEF);
+
+	if (strcmp(device_get_name(device_get_parent(dev)), "isa") == 0)
+		rtype = SYS_RES_IOPORT;
+	else
+		rtype = SYS_RES_MEMORY;
+
 	rid = 0;
-	res = bus_alloc_resource_any(dev, SYS_RES_IOPORT, &rid, RF_ACTIVE);
+	res = bus_alloc_resource_any(dev, rtype, &rid, RF_ACTIVE);
 	if (res == NULL) {
-		device_printf(dev, "could not allocate resources\n");
-		return (ENXIO);
+		device_printf(dev, "cannot allocate resources\n");
+		error = ENXIO;
+		goto fail_mtx;
 	}
 	sc->sc_bst = rman_get_bustag(res);
 	sc->sc_bsh = rman_get_bushandle(res);
@@ -168,7 +172,7 @@ rtc_attach(device_t dev)
 	sc->sc_flag = MC146818_NO_CENT_ADJUST;
 	if ((error = mc146818_attach(dev)) != 0) {
 		device_printf(dev, "cannot attach time of day clock\n");
-		return (error);
+		goto fail_res;
 	}
 
 	if (bootverbose) {
@@ -178,4 +182,11 @@ rtc_attach(device_t dev)
         }
 
 	return (0);
+
+ fail_res:
+	bus_release_resource(dev, rtype, rid, res);
+ fail_mtx:
+	mtx_destroy(&sc->sc_mtx);
+
+	return (error);
 }