netdev - Re: [PATCH] fec: Allow changing the PPS channel

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Date:   Tue, 9 Aug 2022 13:52:54 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Csókás Bence <Csokas.Bence@...lan.hu>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] fec: Allow changing the PPS channel

On Tue, Aug 09, 2022 at 07:36:55AM +0000, Csókás Bence wrote:
> > Don't use a private, custom sysfs knob.  The core PTP layer provides
> > an API for that already.
> 
> Does it? I seem to have missed it. Can you point me at some docs?

See include/uapi/linux/ptp_clock.h:

/*
 * Bits of the ptp_perout_request.flags field:
 */
#define PTP_PEROUT_ONE_SHOT		(1<<0)
#define PTP_PEROUT_DUTY_CYCLE		(1<<1)
#define PTP_PEROUT_PHASE		(1<<2)

/*
 * flag fields valid for the new PTP_PEROUT_REQUEST2 ioctl.
 */
#define PTP_PEROUT_VALID_FLAGS		(PTP_PEROUT_ONE_SHOT | \
					 PTP_PEROUT_DUTY_CYCLE | \
					 PTP_PEROUT_PHASE)

...

struct ptp_perout_request {
	union {
		/*
		 * Absolute start time.
		 * Valid only if (flags & PTP_PEROUT_PHASE) is unset.
		 */
		struct ptp_clock_time start;
		/*
		 * Phase offset. The signal should start toggling at an
		 * unspecified integer multiple of the period, plus this value.
		 * The start time should be "as soon as possible".
		 * Valid only if (flags & PTP_PEROUT_PHASE) is set.
		 */
		struct ptp_clock_time phase;
	};
	struct ptp_clock_time period; /* Desired period, zero means disable. */
	unsigned int index;           /* Which channel to configure. */
	unsigned int flags;
	union {
		/*
		 * The "on" time of the signal.
		 * Must be lower than the period.
		 * Valid only if (flags & PTP_PEROUT_DUTY_CYCLE) is set.
		 */
		struct ptp_clock_time on;
		/* Reserved for future use. */
		unsigned int rsv[4];
	};
};


There is also an API to select pins, with ptp_pin_function,
ptp_pin_desc, PTP_PIN_GETFUNC, PTP_PIN_SETFUNC.

> Also, does it have support for setting pulse mode (i.e. high, low, toggle)?

You can produce a signal with any duty cycle that you wish.  No
support for inverted output, but you could add it if it is important
to you.

Thanks,
Richard