Messages in this thread | | | Date | Mon, 2 Mar 2020 18:01:48 -0800 | From | "Christopher S. Hall" <> | Subject | Re: [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO Driver with PHC interface changes to support additional H/W Features |
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Hi Richard,
On Tue, Feb 25, 2020 at 06:47:07PM -0800, Richard Cochran wrote: > On Tue, Feb 25, 2020 at 03:37:07PM -0800, Christopher S. Hall wrote: > > On Sun, Feb 02, 2020 at 08:08:38PM -0800, Richard Cochran wrote: > > > The TGPIO input clock, the ART, is a free running counter, but you > > > want to support frequency adjustments. Use a timecounter cyclecounter > > > pair. > > > > I'm concerned about the complexity that the timecounter adds to > > the driver. Specifically, the complexity of dealing with any rate mismatches > > between the timecounter and the periodic output signal. The phase > > error between the output and timecounter needs to be zero. > > If I understood correctly, the device's outputs are generated from a > non-adjustable counter. So, no matter what, you will have the problem > of changing the pulse period in concert with the user changing the > desired frequency. >
> > This leaves the PHC API behavior as it is currently and uses the frequency > > adjust API to adjust the output rate. > > > > > Let the user dial a periodic output signal in the normal way. > > > > > > Let the user change the frequency in the normal way, and during this > > > call, adjust the counter values accordingly. > > > > Yes to both of the above. > > So, why then do you need this? > > +#define PTP_EVENT_COUNT_TSTAMP2 \ > + _IOWR(PTP_CLK_MAGIC, 19, struct ptp_event_count_tstamp) > > If you can make the device work with the existing user space API, > > ioctl(fd, PTP_PEROUT_REQUEST2, ...); > while (1) { > clock_adjtimex(FD_TO_CLOCKID(fd), ...); > } > > that would be ideal. But I will push back on anything like the > following. > > ioctl(fd, PTP_PEROUT_REQUEST2, ...); > while (1) { > clock_adjtimex(FD_TO_CLOCKID(fd), ...); > ioctl(fd, PTP_EVENT_COUNT_TSTAMP, ...); > } > > But maybe I misunderstood?
Thank you for the feedback, but Thomas wants to see this as an extension of GPIO. I'll work on an RFC patch for that instead.
> Thanks, > Richard
Thanks, Christopher
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