diff --git a/clock.c b/clock.c
index 56bc79b..9c493c3 100644
--- a/clock.c
+++ b/clock.c
@@ -979,8 +979,7 @@ struct clock *clock_create(enum clock_type type, struct config *config,
 		phc_index = -1;
 	} else if (phc_device) {
 		if (1 != sscanf(phc_device, "/dev/ptp%d", &phc_index)) {
-			pr_err("bad ptp device string");
-			return NULL;
+			phc_index = -1;
 		}
 	} else if (iface->ts_info.valid) {
 		phc_index = iface->ts_info.phc_index;
@@ -1053,6 +1052,14 @@ struct clock *clock_create(enum clock_type type, struct config *config,
 			return NULL;
 		}
 		clockadj_init(c->clkid);
+	} else if (phc_device) {
+		c->clkid = phc_open(phc_device);
+		if (c->clkid == CLOCK_INVALID) {
+			pr_err("Failed to open %s: %m", phc_device);
+			return NULL;
+		}
+		max_adj = clockadj_max_freq(c->clkid);
+		clockadj_init(c->clkid);
 	} else {
 		c->clkid = CLOCK_REALTIME;
 		c->utc_timescale = 1;
diff --git a/clockadj.c b/clockadj.c
index 86c7b33..0485d8c 100644
--- a/clockadj.c
+++ b/clockadj.c
@@ -103,6 +103,30 @@ void clockadj_step(clockid_t clkid, int64_t step)
 		pr_err("failed to step clock: %m");
 }
 
+int clockadj_max_freq(clockid_t clkid)
+{
+	int f = 0;
+	struct timex tx;
+
+	memset(&tx, 0, sizeof(tx));
+	if (clock_adjtime(clkid, &tx) < 0)
+		pr_err("failed to read out the clock maximum adjustment: %m");
+	else
+		f = tx.tolerance / 65.536;
+	if (!f)
+		f = 500000;
+
+	/* The kernel allows the tick length to be adjusted up to 10%. But use
+	 * it only if the overall frequency of the clock can be adjusted
+	 * continuously with the tick and freq fields (i.e. hz <= 1000).
+	 */
+	if (clkid == CLOCK_REALTIME && (realtime_nominal_tick && 2 * f >=
+					1000 * realtime_hz))
+		f = realtime_nominal_tick / 10 * 1000 * realtime_hz;
+
+	return f;
+}
+
 void sysclk_set_leap(int leap)
 {
 	clockid_t clkid = CLOCK_REALTIME;
@@ -142,24 +166,7 @@ void sysclk_set_tai_offset(int offset)
 
 int sysclk_max_freq(void)
 {
-	clockid_t clkid = CLOCK_REALTIME;
-	int f = 0;
-	struct timex tx;
-	memset(&tx, 0, sizeof(tx));
-	if (clock_adjtime(clkid, &tx) < 0)
-		pr_err("failed to read out the clock maximum adjustment: %m");
-	else
-		f = tx.tolerance / 65.536;
-	if (!f)
-		f = 500000;
-
-	/* The kernel allows the tick length to be adjusted up to 10%. But use
-	   it only if the overall frequency of the clock can be adjusted
-	   continuously with the tick and freq fields (i.e. hz <= 1000). */
-	if (realtime_nominal_tick && 2 * f >= 1000 * realtime_hz)
-		f = realtime_nominal_tick / 10 * 1000 * realtime_hz;
-
-	return f;
+	return clockadj_max_freq(CLOCK_REALTIME);
 }
 
 void sysclk_set_sync(void)
diff --git a/clockadj.h b/clockadj.h
index 492418e..4ea98c1 100644
--- a/clockadj.h
+++ b/clockadj.h
@@ -50,6 +50,12 @@ double clockadj_get_freq(clockid_t clkid);
  */
 void clockadj_step(clockid_t clkid, int64_t step);
 
+/**
+ * Read maximum frequency adjustment of the target clock.
+ * @return The maximum frequency adjustment in parts per billion (ppb).
+ */
+int clockadj_max_freq(clockid_t clkid);
+
 /**
  * Set the system clock to insert/delete leap second at midnight.
  * @param leap  +1 to insert leap second, -1 to delete leap second,
diff --git a/phc.c b/phc.c
index 40fa6a1..a90d13e 100644
--- a/phc.c
+++ b/phc.c
@@ -16,11 +16,12 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
-#include <stdio.h>
-#include <sys/ioctl.h>
-#include <sys/types.h>
-#include <sys/stat.h>
 #include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 #include <unistd.h>
 
 #include <linux/ptp_clock.h>
@@ -38,18 +39,26 @@
 
 static int phc_get_caps(clockid_t clkid, struct ptp_clock_caps *caps);
 
-clockid_t phc_open(char *phc)
+clockid_t phc_open(const char *phc)
 {
 	clockid_t clkid;
-	struct ptp_clock_caps caps;
-	int fd = open(phc, O_RDWR);
+	struct timespec ts;
+	struct timex tx;
+	int fd;
 
+	memset(&tx, 0, sizeof(tx));
+
+	fd = open(phc, O_RDWR);
 	if (fd < 0)
 		return CLOCK_INVALID;
 
 	clkid = FD_TO_CLOCKID(fd);
 	/* check if clkid is valid */
-	if (phc_get_caps(clkid, &caps)) {
+	if (clock_gettime(clkid, &ts)) {
+		close(fd);
+		return CLOCK_INVALID;
+	}
+	if (clock_adjtime(clkid, &tx)) {
 		close(fd);
 		return CLOCK_INVALID;
 	}
diff --git a/phc.h b/phc.h
index 154e35e..c0c5996 100644
--- a/phc.h
+++ b/phc.h
@@ -28,7 +28,7 @@
  *
  * @return A valid clock ID on success, CLOCK_INVALID otherwise.
  */
-clockid_t phc_open(char *phc);
+clockid_t phc_open(const char *phc);
 
 /**
  * Closes a PTP hardware clock device.
diff --git a/ptp4l.c b/ptp4l.c
index 3a9f084..17db31f 100644
--- a/ptp4l.c
+++ b/ptp4l.c
@@ -56,7 +56,7 @@ static void usage(char *progname)
 		" -f [file] read configuration from 'file'\n"
 		" -i [dev]  interface device to use, for example 'eth0'\n"
 		"           (may be specified multiple times)\n"
-		" -p [dev]  PTP hardware clock device to use, default auto\n"
+		" -p [dev]  Clock device to use, default auto\n"
 		"           (ignored for SOFTWARE/LEGACY HW time stamping)\n"
 		" -s        slave only mode (overrides configuration file)\n"
 		" -t        transparent clock\n"