diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
index bf6468c56419c..4380e6ddb8495 100644
--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c
@@ -205,6 +205,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd,
 
 	case PTP_EXTTS_REQUEST:
 	case PTP_EXTTS_REQUEST2:
+		if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) {
+			err = -EACCES;
+			break;
+		}
 		memset(&req, 0, sizeof(req));
 
 		if (copy_from_user(&req.extts, (void __user *)arg,
@@ -246,6 +250,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd,
 
 	case PTP_PEROUT_REQUEST:
 	case PTP_PEROUT_REQUEST2:
+		if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) {
+			err = -EACCES;
+			break;
+		}
 		memset(&req, 0, sizeof(req));
 
 		if (copy_from_user(&req.perout, (void __user *)arg,
@@ -314,6 +322,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd,
 
 	case PTP_ENABLE_PPS:
 	case PTP_ENABLE_PPS2:
+		if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) {
+			err = -EACCES;
+			break;
+		}
 		memset(&req, 0, sizeof(req));
 
 		if (!capable(CAP_SYS_TIME))
@@ -456,6 +468,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd,
 
 	case PTP_PIN_SETFUNC:
 	case PTP_PIN_SETFUNC2:
+		if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) {
+			err = -EACCES;
+			break;
+		}
 		if (copy_from_user(&pd, (void __user *)arg, sizeof(pd))) {
 			err = -EFAULT;
 			break;
diff --git a/include/linux/posix-clock.h b/include/linux/posix-clock.h
index ef8619f489203..a500d3160fe8c 100644
--- a/include/linux/posix-clock.h
+++ b/include/linux/posix-clock.h
@@ -95,10 +95,13 @@ struct posix_clock {
  * struct posix_clock_context - represents clock file operations context
  *
  * @clk:              Pointer to the clock
+ * @fp:               Pointer to the file used to open the clock
  * @private_clkdata:  Pointer to user data
  *
  * Drivers should use struct posix_clock_context during specific character
- * device file operation methods to access the posix clock.
+ * device file operation methods to access the posix clock. In particular,
+ * the file pointer can be used to verify correct access mode for ioctl()
+ * calls.
  *
  * Drivers can store a private data structure during the open operation
  * if they have specific information that is required in other file
@@ -106,6 +109,7 @@ struct posix_clock {
  */
 struct posix_clock_context {
 	struct posix_clock *clk;
+	struct file *fp;
 	void *private_clkdata;
 };
 
diff --git a/kernel/time/posix-clock.c b/kernel/time/posix-clock.c
index 1af0bb2cc45c0..fe963384d5c2a 100644
--- a/kernel/time/posix-clock.c
+++ b/kernel/time/posix-clock.c
@@ -129,6 +129,7 @@ static int posix_clock_open(struct inode *inode, struct file *fp)
 		goto out;
 	}
 	pccontext->clk = clk;
+	pccontext->fp = fp;
 	if (clk->ops.open) {
 		err = clk->ops.open(pccontext, fp->f_mode);
 		if (err) {
@@ -251,7 +252,7 @@ static int pc_clock_adjtime(clockid_t id, struct __kernel_timex *tx)
 	if (err)
 		return err;
 
-	if ((cd.fp->f_mode & FMODE_WRITE) == 0) {
+	if (tx->modes && (cd.fp->f_mode & FMODE_WRITE) == 0) {
 		err = -EACCES;
 		goto out;
 	}
diff --git a/tools/testing/selftests/ptp/testptp.c b/tools/testing/selftests/ptp/testptp.c
index 58064151f2c89..edc08a4433fd4 100644
--- a/tools/testing/selftests/ptp/testptp.c
+++ b/tools/testing/selftests/ptp/testptp.c
@@ -140,6 +140,7 @@ static void usage(char *progname)
 		" -H val     set output phase to 'val' nanoseconds (requires -p)\n"
 		" -w val     set output pulse width to 'val' nanoseconds (requires -p)\n"
 		" -P val     enable or disable (val=1|0) the system clock PPS\n"
+		" -r         open the ptp clock in readonly mode\n"
 		" -s         set the ptp clock time from the system time\n"
 		" -S         set the system time from the ptp clock time\n"
 		" -t val     shift the ptp clock time by 'val' seconds\n"
@@ -188,6 +189,7 @@ int main(int argc, char *argv[])
 	int pin_index = -1, pin_func;
 	int pps = -1;
 	int seconds = 0;
+	int readonly = 0;
 	int settime = 0;
 	int channel = -1;
 	clockid_t ext_clockid = CLOCK_REALTIME;
@@ -200,7 +202,7 @@ int main(int argc, char *argv[])
 
 	progname = strrchr(argv[0], '/');
 	progname = progname ? 1+progname : argv[0];
-	while (EOF != (c = getopt(argc, argv, "cd:e:f:F:ghH:i:k:lL:n:o:p:P:sSt:T:w:x:Xy:z"))) {
+	while (EOF != (c = getopt(argc, argv, "cd:e:f:F:ghH:i:k:lL:n:o:p:P:rsSt:T:w:x:Xy:z"))) {
 		switch (c) {
 		case 'c':
 			capabilities = 1;
@@ -252,6 +254,9 @@ int main(int argc, char *argv[])
 		case 'P':
 			pps = atoi(optarg);
 			break;
+		case 'r':
+			readonly = 1;
+			break;
 		case 's':
 			settime = 1;
 			break;
@@ -308,7 +313,7 @@ int main(int argc, char *argv[])
 		}
 	}
 
-	fd = open(device, O_RDWR);
+	fd = open(device, readonly ? O_RDONLY : O_RDWR);
 	if (fd < 0) {
 		fprintf(stderr, "opening %s: %s\n", device, strerror(errno));
 		return -1;
@@ -436,14 +441,16 @@ int main(int argc, char *argv[])
 	}
 
 	if (extts) {
-		memset(&extts_request, 0, sizeof(extts_request));
-		extts_request.index = index;
-		extts_request.flags = PTP_ENABLE_FEATURE;
-		if (ioctl(fd, PTP_EXTTS_REQUEST, &extts_request)) {
-			perror("PTP_EXTTS_REQUEST");
-			extts = 0;
-		} else {
-			puts("external time stamp request okay");
+		if (!readonly) {
+			memset(&extts_request, 0, sizeof(extts_request));
+			extts_request.index = index;
+			extts_request.flags = PTP_ENABLE_FEATURE;
+			if (ioctl(fd, PTP_EXTTS_REQUEST, &extts_request)) {
+				perror("PTP_EXTTS_REQUEST");
+				extts = 0;
+			} else {
+				puts("external time stamp request okay");
+			}
 		}
 		for (; extts; extts--) {
 			cnt = read(fd, &event, sizeof(event));
@@ -455,10 +462,12 @@ int main(int argc, char *argv[])
 			       event.t.sec, event.t.nsec);
 			fflush(stdout);
 		}
-		/* Disable the feature again. */
-		extts_request.flags = 0;
-		if (ioctl(fd, PTP_EXTTS_REQUEST, &extts_request)) {
-			perror("PTP_EXTTS_REQUEST");
+		if (!readonly) {
+			/* Disable the feature again. */
+			extts_request.flags = 0;
+			if (ioctl(fd, PTP_EXTTS_REQUEST, &extts_request)) {
+				perror("PTP_EXTTS_REQUEST");
+			}
 		}
 	}