> -----Original Message-----
> From: Keller, Jacob E
> Sent: Tuesday, September 24, 2019 12:23 PM
> To: Felipe Balbi <[email protected]>; Richard Cochran
> <[email protected]>
> Cc: Hall, Christopher S <[email protected]>;
> [email protected]; [email protected]
> Subject: RE: [PATCH v4 2/2] PTP: add support for one-shot output
>
>
>
> > -----Original Message-----
> > From: [email protected] [mailto:[email protected]]
> On
> > Behalf Of Felipe Balbi
> > Sent: Tuesday, September 10, 2019 11:16 PM
> > To: Richard Cochran <[email protected]>
> > Cc: Hall, Christopher S <[email protected]>;
> [email protected];
> > [email protected]; Felipe Balbi
> <[email protected]>
> > Subject: [PATCH v4 2/2] PTP: add support for one-shot output
> >
> > Some controllers allow for a one-shot output pulse, in contrast to
> > periodic output. Now that we have extensible versions of our IOCTLs, we
> > can finally make use of the 'flags' field to pass a bit telling driver
> > that if we want one-shot pulse output.
> >
> > Signed-off-by: Felipe Balbi <[email protected]>
> > ---
> >
> > Changes since v3:
> > - Remove bogus bitwise negation
> >
> > Changes since v2:
> > - Add _PEROUT_ to bit macro
> >
> > Changes since v1:
> > - remove comment from .flags field
> >
> > include/uapi/linux/ptp_clock.h | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/uapi/linux/ptp_clock.h
> b/include/uapi/linux/ptp_clock.h
> > index 9a0af3511b68..f16301015949 100644
> > --- a/include/uapi/linux/ptp_clock.h
> > +++ b/include/uapi/linux/ptp_clock.h
> > @@ -38,8 +38,8 @@
> > /*
> > * Bits of the ptp_perout_request.flags field:
> > */
> > -#define PTP_PEROUT_VALID_FLAGS (0)
> > -
> > +#define PTP_PEROUT_ONE_SHOT (1<<0)
> > +#define PTP_PEROUT_VALID_FLAGS (PTP_PEROUT_ONE_SHOT)
> > /*
> > * struct ptp_clock_time - represents a time value
> > *
> > @@ -77,7 +77,7 @@ 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. */
> > + unsigned int flags;
> > unsigned int rsv[4]; /* Reserved for future use. */
> > };
> >
> > --
> > 2.23.0
>
> Hi Felipe,
>
> Do you have any examples for how you envision using this? I don't see any
> drivers or other code on the list for doing so.
>
> Additionally, it seems weird because we do not have support for specifying
> the pulse width. I guess you leave that up to driver choice?
>
> Thanks,
> Jake
Jake,
Good catch on the terminology. This is an API that produces edges not pulses.
This flag causes the PEROUT ioctl to ignore the period argument and produce a
single edge. Currently, the igb driver implements the same function, but uses
a "magic" invalid period specification to signal that the period argument
should be ignored (use_freq == 0):
if (on && ((ns <= 70000000LL) || (ns == 125000000LL) ||
(ns == 250000000LL) || (ns == 500000000LL))) {
if (ns < 8LL)
return -EINVAL;
use_freq = 1;
}
The proposal is to support this function without magic period specifications
using an explicit flag instead. An example use case is pulse-per-second
output. While PPS is periodic, time-aware GPIO is driven by (an
unadjustable) Always Running Timer (ART). It's necessary to schedule each
edge in software to produce PPS synced with system time.
Chris
