mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2024-11-21 19:46:16 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

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

Browse Source 
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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];
};