On Tue, Aug 27, 2024 at 03:09:15PM +0200, Rodolfo Giometti wrote: > On 24/08/24 04:21, Greg KH wrote: > > On Fri, Aug 23, 2024 at 12:31:07PM +0530, subramanian.mohan@xxxxxxxxx wrote: > > > From: Subramanian Mohan <subramanian.mohan@xxxxxxxxx> > > > > > > Add Intel Timed I/O PPS usage instructions. > > > > > > Co-developed-by: Pandith N <pandith.n@xxxxxxxxx> > > > Signed-off-by: Pandith N <pandith.n@xxxxxxxxx> > > > Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx> > > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > > > Acked-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx> > > > Signed-off-by: Subramanian Mohan <subramanian.mohan@xxxxxxxxx> > > > --- > > > Documentation/driver-api/pps.rst | 24 ++++++++++++++++++++++++ > > > 1 file changed, 24 insertions(+) > > > > > > diff --git a/Documentation/driver-api/pps.rst b/Documentation/driver-api/pps.rst > > > index 78dded03e5d8..75f7b094f963 100644 > > > --- a/Documentation/driver-api/pps.rst > > > +++ b/Documentation/driver-api/pps.rst > > > @@ -246,3 +246,27 @@ delay between assert and clear edge as small as possible to reduce system > > > latencies. But if it is too small slave won't be able to capture clear edge > > > transition. The default of 30us should be good enough in most situations. > > > The delay can be selected using 'delay' pps_gen_parport module parameter. > > > + > > > + > > > +Intel Timed I/O PPS signal generator > > > +------------------------------------ > > > + > > > +Intel Timed I/O is a high precision device, present on 2019 and newer Intel > > > +CPUs, that can generate PPS signals. > > > + > > > +Timed I/O and system time are both driven by same hardware clock. The signal > > > +is generated with a precision of ~20 nanoseconds. The generated PPS signal > > > +is used to synchronize an external device with system clock. For example, > > > +it can be used to share your clock with a device that receives PPS signal, > > > +generated by Timed I/O device. There are dedicated Timed I/O pins to deliver > > > +the PPS signal to an external device. > > > + > > > +Usage of Intel Timed I/O as PPS generator: > > > + > > > +Start generating PPS signal:: > > > + > > > + $echo 1 > /sys/devices/platform/INTCxxxx\:00/enable > > > + > > > +Stop generating PPS signal:: > > > + > > > + $echo 0 > /sys/devices/platform/INTCxxxx\:00/enable > > > > As I mentioned on the sysfs documentation, why isn't this just a generic > > pps class attribute instead? Why did you make it > > only-this-one-special-driver type of thing? > > This is an Original Sin when PPS generators were introduced. :-( > > In 2011 a patch from Alexander Gordeev <lasaine@xxxxxxxxxxxxx> (which > introduced the "parallel port PPS signal generator") was committed in the > main kernel. > > At the time it was something exotic and doing a PPS generator interface for > it was not considered (since it actually has no controlling inputs), but now > several Ethernet cards have such PPS generator functionalities, and they are > enabled in a per-driver way or via the PTP API. > > This code is a pure PPS generator and it cannot use any other way to enable > such functionality than the one above since the PPS layer misses a proper > implementation for PPS generator. > > If you are willing to stop the inclusion due this fact maybe its time to add > such PPS generators interface... on the other hand, if you agree for > inclusion we can do this job as soon as the code has been included, in order > to fix this anomalous status. Please make a generic pps subsystem for this, it would make it simpler for everyone. thanks, greg k-h
