diff mbox series

[net-next,v5] ptp/ioctl: support MONOTONIC{,_RAW} timestamps for PTP_SYS_OFFSET_EXTENDED

Message ID 20240904141305.2856789-1-vadfed@meta.com (mailing list archive)
State Accepted
Commit c259acab839e57eab0318f32da4ae803a8d59397
Delegated to: Netdev Maintainers
Headers show
Series [net-next,v5] ptp/ioctl: support MONOTONIC{,_RAW} timestamps for PTP_SYS_OFFSET_EXTENDED | expand

Checks

Context Check Description
netdev/series_format success Single patches do not need cover letters
netdev/tree_selection success Clearly marked for net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 18 this patch: 18
netdev/build_tools success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers success CCed 3 of 3 maintainers
netdev/build_clang success Errors and warnings before: 20 this patch: 20
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 238 this patch: 238
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 104 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 8 this patch: 8
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-09-06--21-00 (tests: 721)

Commit Message

Vadim Fedorenko Sept. 4, 2024, 2:13 p.m. UTC 
From: Mahesh Bandewar <maheshb@google.com>

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>
---
As Mahesh is not responding for more then a week, and there were no
new versions from May 2024, I decided to continue the work as we
found this feature useful in our case too. I'll keep previous change
log as is, but put the latest on top:

v4 -> v5:
- rebase on top of current net-next
- add CLOCK_MONOTONIC as another option (suggest by Richard)
- adjusted comment about changes in the ptp_sys_offset_extended
- reasoning explanation is done by Yuliang Li, link:
https://lore.kernel.org/netdev/CADj8K+M9qjLGAKcsV_9YoPQ5SGXe3vmi69Y65m1RUyLOMrJeHg@mail.gmail.com/

Original changelog:

v1 -> v2
   * Code-style fixes.
v2 -> v3
   * Reword commit log
   * Fix the compilation issue by using __kernel_clockid instead of clockid_t
     which has kernel only scope.
v3 -> v4
   * Typo/comment fixes.

 drivers/ptp/ptp_chardev.c        |  8 +++++--
 include/linux/ptp_clock_kernel.h | 36 ++++++++++++++++++++++++++++----
 include/uapi/linux/ptp_clock.h   | 24 +++++++++++++++------
 3 files changed, 56 insertions(+), 12 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Sept. 8, 2024, 5:50 p.m. UTC | #1 
Hello:

This patch was applied to netdev/net-next.git (main)
by David S. Miller <davem@davemloft.net>:

On Wed, 4 Sep 2024 07:13:05 -0700 you wrote:
> From: Mahesh Bandewar <maheshb@google.com>
> 
> 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.
> 
> [...]

Here is the summary with links:
  - [net-next,v5] ptp/ioctl: support MONOTONIC{,_RAW} timestamps for PTP_SYS_OFFSET_EXTENDED
    https://git.kernel.org/netdev/net-next/c/c259acab839e

You are awesome, thank you!
diff mbox series

Patch

diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
index 2067b0120d08..ea96a14d72d1 100644
--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c
@@ -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)
diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
index 6e4b8206c7d0..c892d22ce0a7 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -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
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];
 };