ptp: add pseudo pps ioctl

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.

Quoted 6 lines · Richard Cochran

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.

Would it make sense to extend the ioctl to allow also comparing the PHC with another PHC or perhaps even a different system clock than CLOCK_REALTIME?

I'm thinking if someone wanted to synchronize one PHC to another, it should be better to work with phc1-phc2 offsets than combine phc1-sys and sys-phc2 offsets.

I am guessing it would be possible to synchronize two PHC devices to within a few microseconds this way. Probably that is not good enough to implement a boundary clock, for example, so I have my doubts about the utility of this.

But in any case, it is possible, and I think that
feature can wait for now.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Richard Cochran
Sent: Thursday, September 27, 2012 11:12 AM
To: [email protected]
Cc: David Miller; Keller, Jacob E; John Stultz; Miroslav Lichvar
Subject: [PATCH RFC net-next 1/1] 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 <[email protected]>

---
 drivers/ptp/ptp_chardev.c |   32 ++++++++++++++++++++++++++++++++
 include/linux/ptp_clock.h |   14 ++++++++++++++
 2 files changed, 46 insertions(+), 0 deletions(-)

drivers/ptp/ptp_chardev.c index renamed from drivers/ptp/ptp_chardev.c +0 -0

e7f301da2..4f8ae80 100644

drivers/ptp/ptp_chardev.c +32 -0

@@ -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:

drivers/ptp/ptp_chardev.c +0 -0

 		err = -ENOTTY;
 		break;

include/linux/ptp_clock.h index renamed from include/linux/ptp_clock.h +0 -0

94e981f..b65c834 100644

include/linux/ptp_clock.h +14 -0

@@ -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. */
--
1.7.2.5

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