Index: head/share/man/man4/man4.powerpc/powermac_nvram.4
===================================================================
--- head/share/man/man4/man4.powerpc/powermac_nvram.4
+++ head/share/man/man4/man4.powerpc/powermac_nvram.4
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 5, 2010
+.Dd June 19, 2020
 .Dt POWERMAC_NVRAM 4 powerpc
 .Os
 .Sh NAME
@@ -50,8 +50,10 @@
 .Nm
 driver provides access to the Open Firmware configuration NVRAM
 available on the Apple PowerPC-based machines.
+.Pp
+This driver currently supports "Core99" machines containing a Sharp, Micron,
+or AMD NVRAM.
 .Sh SEE ALSO
-.Xr eeprom 8 ,
 .Xr nvram 8
 .Sh HISTORY
 The
Index: head/sys/dev/powermac_nvram/powermac_nvram.c
===================================================================
--- head/sys/dev/powermac_nvram/powermac_nvram.c
+++ head/sys/dev/powermac_nvram/powermac_nvram.c
@@ -34,6 +34,8 @@
 #include <sys/bus.h>
 #include <sys/conf.h>
 #include <sys/kernel.h>
+#include <sys/lock.h>
+#include <sys/sx.h>
 #include <sys/uio.h>
 
 #include <dev/ofw/openfirm.h>
@@ -99,7 +101,6 @@
 
 static struct cdevsw powermac_nvram_cdevsw = {
 	.d_version =	D_VERSION,
-	.d_flags =	D_NEEDGIANT,
 	.d_open =	powermac_nvram_open,
 	.d_close =	powermac_nvram_close,
 	.d_read =	powermac_nvram_read,
@@ -180,6 +181,8 @@
 	    "powermac_nvram");
 	sc->sc_cdev->si_drv1 = sc;
 
+	sx_init(&sc->sc_lock, "powermac_nvram");
+
 	return 0;
 }
 
@@ -195,6 +198,8 @@
 
 	if (sc->sc_cdev != NULL)
 		destroy_dev(sc->sc_cdev);
+
+	sx_destroy(&sc->sc_lock);
 	
 	return 0;
 }
@@ -203,11 +208,17 @@
 powermac_nvram_open(struct cdev *dev, int flags, int fmt, struct thread *td)
 {
 	struct powermac_nvram_softc *sc = dev->si_drv1;
+	int err;
 
+	err = 0;
+	sx_xlock(&sc->sc_lock);
 	if (sc->sc_isopen)
-		return EBUSY;
-	sc->sc_isopen = 1;
+		err = EBUSY;
+	else
+		sc->sc_isopen = 1;
 	sc->sc_rpos = sc->sc_wpos = 0;
+	sx_xunlock(&sc->sc_lock);
+
 	return 0;
 }
 
@@ -218,10 +229,12 @@
 	struct core99_header *header;
 	vm_offset_t bank;
 
+	sx_xlock(&sc->sc_lock);
 	if (sc->sc_wpos != sizeof(sc->sc_data)) {
 		/* Short write, restore in-memory copy */
 		bcopy((void *)sc->sc_bank, (void *)sc->sc_data, NVRAM_SIZE);
 		sc->sc_isopen = 0;
+		sx_xunlock(&sc->sc_lock);
 		return 0;
 	}
 
@@ -242,10 +255,12 @@
 	if (erase_bank(sc->sc_dev, (uint8_t *)bank) != 0 ||
 	    write_bank(sc->sc_dev, (uint8_t *)bank, sc->sc_data) != 0) {
 		sc->sc_isopen = 0;
+		sx_xunlock(&sc->sc_lock);
 		return ENOSPC;
 	}
 	sc->sc_bank = bank;
 	sc->sc_isopen = 0;
+	sx_xunlock(&sc->sc_lock);
 	return 0;
 }
 
@@ -256,6 +271,8 @@
 	struct powermac_nvram_softc *sc = dev->si_drv1;
 
 	rv = 0;
+
+	sx_xlock(&sc->sc_lock);
 	while (uio->uio_resid > 0) {
 		data_available = sizeof(sc->sc_data) - sc->sc_rpos;
 		if (data_available > 0) {
@@ -269,6 +286,8 @@
 			break;
 		}
 	}
+	sx_xunlock(&sc->sc_lock);
+
 	return rv;
 }
 
@@ -282,6 +301,8 @@
 		return EINVAL;
 
 	rv = 0;
+
+	sx_xlock(&sc->sc_lock);
 	while (uio->uio_resid > 0) {
 		data_available = sizeof(sc->sc_data) - sc->sc_wpos;
 		if (data_available > 0) {
@@ -295,6 +316,8 @@
 			break;
 		}
 	}
+	sx_xunlock(&sc->sc_lock);
+
 	return rv;
 }
 
@@ -500,6 +523,8 @@
 	struct powermac_nvram_softc *sc;
 
 	sc = device_get_softc(dev);
+
+	sx_assert(&sc->sc_lock, SA_XLOCKED);
 	if (sc->sc_type == FLASH_TYPE_AMD)
 		return (erase_bank_amd(dev, bank));
 	else
@@ -512,6 +537,8 @@
 	struct powermac_nvram_softc *sc;
 
 	sc = device_get_softc(dev);
+
+	sx_assert(&sc->sc_lock, SA_XLOCKED);
 	if (sc->sc_type == FLASH_TYPE_AMD)
 		return (write_bank_amd(dev, bank, data));
 	else
Index: head/sys/dev/powermac_nvram/powermac_nvramvar.h
===================================================================
--- head/sys/dev/powermac_nvram/powermac_nvramvar.h
+++ head/sys/dev/powermac_nvram/powermac_nvramvar.h
@@ -49,6 +49,7 @@
 
 struct powermac_nvram_softc {
 	device_t		sc_dev;
+	struct sx		sc_lock;
 	phandle_t		sc_node;
 	vm_offset_t		sc_bank;
 	vm_offset_t		sc_bank0;
Index: head/usr.sbin/nvram/nvram.8
===================================================================
--- head/usr.sbin/nvram/nvram.8
+++ head/usr.sbin/nvram/nvram.8
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd August 1, 2006
+.Dd June 19, 2020
 .Dt NVRAM 8 powerpc
 .Os
 .Sh NAME
@@ -98,8 +98,7 @@
 .Pp
 .Dl "nvram -d foo -d bar baz=100"
 .Sh SEE ALSO
-.Xr powermac_nvram 4 ,
-.Xr eeprom 8
+.Xr powermac_nvram 4
 .Sh HISTORY
 The
 .Nm
@@ -111,8 +110,3 @@
 utility.
 .Sh AUTHORS
 .An Maxim Sobolev Aq Mt sobomax@FreeBSD.org
-.Sh BUGS
-Currently,
-.Nm
-only supports systems equipped with AMD flash and is only tested on Apple
-G4-based Mac Mini machines.