ptp: add an ioctl to compare PHC time with system time

This patch adds an ioctl for PTP Hardware Clock (PHC) devices that allows
user space to measure the time offset between the PHC and the system
clock. Rather than hard coding any kind of estimation algorithm into the
kernel, this patch takes the more flexible approach of just delivering
an array of raw clock readings. In that way, the user space clock servo
may be adapted to new and different hardware clocks.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/ptp_chardev.c

@@ -33,9 +33,13 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 {
 	struct ptp_clock_caps caps;
 	struct ptp_clock_request req;
+	struct ptp_sys_offset sysoff;
 	struct ptp_clock *ptp = container_of(pc, struct ptp_clock, clock);
 	struct ptp_clock_info *ops = ptp->info;
+	struct ptp_clock_time *pct;
+	struct timespec ts;
 	int enable, err = 0;
+	unsigned int i;
 
 	switch (cmd) {
 
@@ -88,6 +92,34 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 		err = ops->enable(ops, &req, enable);
 		break;
 
+	case PTP_SYS_OFFSET:
+		if (copy_from_user(&sysoff, (void __user *)arg,
+				   sizeof(sysoff))) {
+			err = -EFAULT;
+			break;
+		}
+		if (sysoff.n_samples > PTP_MAX_SAMPLES) {
+			err = -EINVAL;
+			break;
+		}
+		pct = &sysoff.ts[0];
+		for (i = 0; i < sysoff.n_samples; i++) {
+			getnstimeofday(&ts);
+			pct->sec = ts.tv_sec;
+			pct->nsec = ts.tv_nsec;
+			pct++;
+			ptp->info->gettime(ptp->info, &ts);
+			pct->sec = ts.tv_sec;
+			pct->nsec = ts.tv_nsec;
+			pct++;
+		}
+		getnstimeofday(&ts);
+		pct->sec = ts.tv_sec;
+		pct->nsec = ts.tv_nsec;
+		if (copy_to_user((void __user *)arg, &sysoff, sizeof(sysoff)))
+			err = -EFAULT;
+		break;
+
 	default:
 		err = -ENOTTY;
 		break;

include/uapi/linux/ptp_clock.h

@@ -67,12 +67,26 @@ struct ptp_perout_request {
 	unsigned int rsv[4];          /* Reserved for future use. */
 };
 
+#define PTP_MAX_SAMPLES 25 /* Maximum allowed offset measurement samples. */
+
+struct ptp_sys_offset {
+	unsigned int n_samples; /* Desired number of measurements. */
+	unsigned int rsv[3];    /* Reserved for future use. */
+	/*
+	 * Array of interleaved system/phc time stamps. The kernel
+	 * will provide 2*n_samples + 1 time stamps, with the last
+	 * one as a system time stamp.
+	 */
+	struct ptp_clock_time ts[2 * PTP_MAX_SAMPLES + 1];
+};
+
 #define PTP_CLK_MAGIC '='
 
 #define PTP_CLOCK_GETCAPS  _IOR(PTP_CLK_MAGIC, 1, struct ptp_clock_caps)
 #define PTP_EXTTS_REQUEST  _IOW(PTP_CLK_MAGIC, 2, struct ptp_extts_request)
 #define PTP_PEROUT_REQUEST _IOW(PTP_CLK_MAGIC, 3, struct ptp_perout_request)
 #define PTP_ENABLE_PPS     _IOW(PTP_CLK_MAGIC, 4, int)
+#define PTP_SYS_OFFSET     _IOW(PTP_CLK_MAGIC, 5, struct ptp_sys_offset)
 
 struct ptp_extts_event {
 	struct ptp_clock_time t; /* Time event occured. */