linux-kernel - Re: [PATCH v2 2/2] PTP: add support for one-shot output

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Message-ID: <87h85roy9p.fsf@gmail.com>
Date:   Thu, 05 Sep 2019 13:03:46 +0300
From:   Felipe Balbi <felipe.balbi@...ux.intel.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     Christopher S Hall <christopher.s.hall@...el.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        davem@...emloft.net
Subject: Re: [PATCH v2 2/2] PTP: add support for one-shot output


Hi,

Richard Cochran <richardcochran@...il.com> writes:
> On Fri, Aug 30, 2019 at 11:00:20AM +0300, Felipe Balbi wrote:
>> >> @@ -177,9 +177,8 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
>> >>  			err = -EFAULT;
>> >>  			break;
>> >>  		}
>> >> -		if ((req.perout.flags || req.perout.rsv[0] || req.perout.rsv[1]
>> >> -				|| req.perout.rsv[2] || req.perout.rsv[3])
>> >> -			&& cmd == PTP_PEROUT_REQUEST2) {
>> >> +		if ((req.perout.rsv[0] || req.perout.rsv[1] || req.perout.rsv[2]
>> >> +			|| req.perout.rsv[3]) && cmd == PTP_PEROUT_REQUEST2) {
>> >
>> > Please check that the reserved bits of req.perout.flags, namely
>> > ~PTP_PEROUT_ONE_SHOT, are clear.
>> 
>> Actually, we should check more. PEROUT_FEATURE_ENABLE is still valid
>> here, right? So are RISING and FALLING edges, no?
>
> No.  The ptp_extts_request.flags are indeed defined:
>
> struct ptp_extts_request {
> 	...
> 	unsigned int flags;  /* Bit field for PTP_xxx flags. */
> 	...
> };
>
> But the ptp_perout_request.flags are reserved:
>
> struct ptp_perout_request {
> 	...
> 	unsigned int flags;           /* Reserved for future use. */
> 	...
> };

This a bit confusing, really. Specially when the comment right above
those flags states:

/* PTP_xxx bits, for the flags field within the request structures. */

The request "structures" include EXTTS and PEROUT:

struct ptp_clock_request {
	enum {
		PTP_CLK_REQ_EXTTS,
		PTP_CLK_REQ_PEROUT,
		PTP_CLK_REQ_PPS,
	} type;
	union {
		struct ptp_extts_request extts;
		struct ptp_perout_request perout;
	};
};

Seems like we will, at least, make it clear which flags are valid for
which request structures.

> For this ioctl, the test for enable/disable is
> ptp_perout_request.period is zero:
>
> 		enable = req.perout.period.sec || req.perout.period.nsec;
> 		err = ops->enable(ops, &req, enable);
>
> The usage pattern here is taken from timer_settime(2).

got it

-- 
balbi

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