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ptp/ioctl: support MONOTONIC{,_RAW} timestamps for PTP_SYS_OFFSET_EXTENDED

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The ability to read the PHC (Physical Hardware Clock) alongside
multiple system clocks is currently dependent on the specific
hardware architecture. This limitation restricts the use of
PTP_SYS_OFFSET_PRECISE to certain hardware configurations.

The generic soultion which would work across all architectures
is to read the PHC along with the latency to perform PHC-read as
offered by PTP_SYS_OFFSET_EXTENDED which provides pre and post
timestamps.  However, these timestamps are currently limited
to the CLOCK_REALTIME timebase. Since CLOCK_REALTIME is affected
by NTP (or similar time synchronization services), it can
experience significant jumps forward or backward. This hinders
the precise latency measurements that PTP_SYS_OFFSET_EXTENDED
is designed to provide.

This problem could be addressed by supporting MONOTONIC_RAW
timestamps within PTP_SYS_OFFSET_EXTENDED. Unlike CLOCK_REALTIME
or CLOCK_MONOTONIC, the MONOTONIC_RAW timebase is unaffected
by NTP adjustments.

This enhancement can be implemented by utilizing one of the three
reserved words within the PTP_SYS_OFFSET_EXTENDED struct to pass
the clock-id for timestamps.  The current behavior aligns with
clock-id for CLOCK_REALTIME timebase (value of 0), ensuring
backward compatibility of the UAPI.

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Mahesh Bandewar 2024-09-04 07:13:05 -07:00 committed by David S. Miller
parent d5c4546062
commit c259acab83
3 changed files with 56 additions and 12 deletions
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8
drivers/ptp/ptp_chardev.c
View File

@ -359,11 +359,15 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd,
extoff = NULL;
break;
}
if (extoff->n_samples > PTP_MAX_SAMPLES
|| extoff->rsv[0] || extoff->rsv[1] || extoff->rsv[2]) {
if (extoff->n_samples > PTP_MAX_SAMPLES ||
extoff->rsv[0] || extoff->rsv[1] ||
(extoff->clockid != CLOCK_REALTIME &&
extoff->clockid != CLOCK_MONOTONIC &&
extoff->clockid != CLOCK_MONOTONIC_RAW)) {
err = -EINVAL;
break;
}
sts.clockid = extoff->clockid;
for (i = 0; i < extoff->n_samples; i++) {
err = ptp->info->gettimex64(ptp->info, &ts, &sts);
if (err)

36
include/linux/ptp_clock_kernel.h
View File

@ -47,10 +47,12 @@ struct system_device_crosststamp;
* struct ptp_system_timestamp - system time corresponding to a PHC timestamp
* @pre_ts: system timestamp before capturing PHC
* @post_ts: system timestamp after capturing PHC
* @clockid: clock-base used for capturing the system timestamps
*/
struct ptp_system_timestamp {
struct timespec64 pre_ts;
struct timespec64 post_ts;
clockid_t clockid;
};
/**
@ -457,14 +459,40 @@ static inline ktime_t ptp_convert_timestamp(const ktime_t *hwtstamp,
static inline void ptp_read_system_prets(struct ptp_system_timestamp *sts)
{
if (sts)
ktime_get_real_ts64(&sts->pre_ts);
if (sts) {
switch (sts->clockid) {
case CLOCK_REALTIME:
ktime_get_real_ts64(&sts->pre_ts);
break;
case CLOCK_MONOTONIC:
ktime_get_ts64(&sts->pre_ts);
break;
case CLOCK_MONOTONIC_RAW:
ktime_get_raw_ts64(&sts->pre_ts);
break;
default:
break;
}
}
}
static inline void ptp_read_system_postts(struct ptp_system_timestamp *sts)
{
if (sts)
ktime_get_real_ts64(&sts->post_ts);
if (sts) {
switch (sts->clockid) {
case CLOCK_REALTIME:
ktime_get_real_ts64(&sts->post_ts);
break;
case CLOCK_MONOTONIC:
ktime_get_ts64(&sts->post_ts);
break;
case CLOCK_MONOTONIC_RAW:
ktime_get_raw_ts64(&sts->post_ts);
break;
default:
break;
}
}
}
#endif

24
include/uapi/linux/ptp_clock.h
View File

@ -155,13 +155,25 @@ struct ptp_sys_offset {
struct ptp_clock_time ts[2 * PTP_MAX_SAMPLES + 1];
};
/*
* ptp_sys_offset_extended - data structure for IOCTL operation
* PTP_SYS_OFFSET_EXTENDED
*
* @n_samples: Desired number of measurements.
* @clockid: clockid of a clock-base used for pre/post timestamps.
* @rsv: Reserved for future use.
* @ts: Array of samples in the form [pre-TS, PHC, post-TS]. The
* kernel provides @n_samples.
*
* Starting from kernel 6.12 and onwards, the first word of the reserved-field
* is used for @clockid. That's backward compatible since previous kernel
* expect all three reserved words (@rsv[3]) to be 0 while the clockid (first
* word in the new structure) for CLOCK_REALTIME is '0'.
*/
struct ptp_sys_offset_extended {
unsigned int n_samples; /* Desired number of measurements. */
unsigned int rsv[3]; /* Reserved for future use. */
/*
* Array of [system, phc, system] time stamps. The kernel will provide
* 3*n_samples time stamps.
*/
unsigned int n_samples;
__kernel_clockid_t clockid;
unsigned int rsv[2];
struct ptp_clock_time ts[PTP_MAX_SAMPLES][3];
};