Re: [RFC PATCH 4/5] PTP: Add flag for non-periodic output

Richard Cochran
2019-07-16T16:39:33Z

On Tue, Jul 16, 2019 at 10:20:37AM +0300, Felipe Balbi wrote:
> When this new flag is set, we can use single-shot output.
>
> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
> ---
> include/uapi/linux/ptp_clock.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/ptp_clock.h b/include/uapi/linux/ptp_clock.h
> index 674db7de64f3..439cbdfc3d9b 100644
> --- a/include/uapi/linux/ptp_clock.h
> +++ b/include/uapi/linux/ptp_clock.h
> @@ -67,7 +67,9 @@ struct ptp_perout_request {
> struct ptp_clock_time start; /* Absolute start time. */
> struct ptp_clock_time period; /* Desired period, zero means disable. */
> unsigned int index; /* Which channel to configure. */
> - unsigned int flags; /* Reserved for future use. */
> +
> +#define PTP_PEROUT_ONE_SHOT BIT(0)
> + unsigned int flags; /* Bit 0 -> oneshot output. */
> unsigned int rsv[4]; /* Reserved for future use. */

Unfortunately, the code never checked that .flags and .rsv are zero,
and so the de-facto ABI makes extending these fields impossible. That
was my mistake from the beginning.

In order to actually support extensions, you will first have to
introduce a new ioctl.

Sorry,
Richard

> };
>
> --
> 2.22.0
>