Commit 6138e687c7b6 ("ptp: Introduce strict checking of external time stamp options.") added the PTP_STRICT_FLAGS to the set of flags supported for the external timestamp request ioctl. It is only supported by PTP_EXTTS_REQUEST2, as it was introduced the introduction of the new ioctls. Further, the kernel has always set this flag for PTP_EXTTS_REQUEST2 regardless of whether or not the user requested the behavior. This effectively means that the flag is not useful for userspace. If the user issues a PTP_EXTTS_REQUEST ioctl, the flag is ignored due to not being supported on the old ioctl. If the user issues a PTP_EXTTS_REQUEST2 ioctl, the flag will be set by the kernel regardless of whether the user set the flag in their structure. Add a comment documenting this behavior in the uAPI header file. Signed-off-by: Jacob Keller --- include/uapi/linux/ptp_clock.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/include/uapi/linux/ptp_clock.h b/include/uapi/linux/ptp_clock.h index 18eefa6d93d6..2c3346e91dbe 100644 --- a/include/uapi/linux/ptp_clock.h +++ b/include/uapi/linux/ptp_clock.h @@ -37,6 +37,9 @@ /* * flag fields valid for the new PTP_EXTTS_REQUEST2 ioctl. + * + * Note: PTP_STRICT_FLAGS is always enabled by the kernel for + * PTP_EXTTS_REQUEST2 regardless of whether it is set by userspace. */ #define PTP_EXTTS_VALID_FLAGS (PTP_ENABLE_FEATURE | \ PTP_RISING_EDGE | \ -- 2.51.0.rc1.197.g6d975e95c9d7