From c259acab839e57eab0318f32da4ae803a8d59397 Mon Sep 17 00:00:00 2001 From: Mahesh Bandewar Date: Wed, 4 Sep 2024 07:13:05 -0700 Subject: ptp/ioctl: support MONOTONIC{,_RAW} timestamps for PTP_SYS_OFFSET_EXTENDED 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 Signed-off-by: Vadim Fedorenko Signed-off-by: David S. Miller --- include/uapi/linux/ptp_clock.h | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/ptp_clock.h b/include/uapi/linux/ptp_clock.h index 053b40d642de..18eefa6d93d6 100644 --- a/include/uapi/linux/ptp_clock.h +++ b/include/uapi/linux/ptp_clock.h @@ -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]; }; -- cgit v1.2.3