linux-kernel - Re: [PATCH v4 3/4] Add PTP_SYS_OFFSET_PRECISE for driver crosstimestamping

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Message-ID: <op.x7pkjvdk1774gr@chall-mobl2.amr.corp.intel.com>
Date:	Fri, 06 Nov 2015 18:15:21 -0800
From:	"Christopher Hall" <christopher.s.hall@...el.com>
To:	"Richard Cochran" <richardcochran@...il.com>,
	"Thomas Gleixner" <tglx@...utronix.de>
Cc:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"john.stultz@...aro.org" <john.stultz@...aro.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Stanton, Kevin B" <kevin.b.stanton@...el.com>
Subject: Re: [PATCH v4 3/4] Add PTP_SYS_OFFSET_PRECISE for driver
 crosstimestamping

Richard/Thomas:

On Tue, 13 Oct 2015 06:59:26 -0700, Richard Cochran  
<richardcochran@...il.com> wrote:
> On Mon, Oct 12, 2015 at 11:45:21AM -0700, Christopher S. Hall wrote:
>>
>> +struct ptp_sys_offset_precise {
>> +	unsigned int rsv[4];    /* Reserved for future use. */
>> +	struct ptp_clock_time dev;
>> +	struct ptp_clock_time sys;
>> +};
>> +
>
> Please put the reserved field at the bottom.  Also, since we reading
> the raw monotonic time under the hood, we might as well return it in
> this struct too.  It costs us almost nothing, and having that value
> can be useful for characterizing the system oscillator.

Below is my proposal to implement your suggested changes adding monotonic  
raw to the PTP_SYS_OFFSET_PRECISE ioctl:

Move the reserved field to the end and add monotonic raw to
ptp_sys_offset_precise:

struct ptp_sys_offset_precise {
          struct ptp_clock_time dev;
          struct ptp_clock_time sys_real;
          struct ptp_clock_time sys_raw;
          unsigned int rsv[4];    /* Reserved for future use. */
};

In my previous patch, the getsynctime() prototype is:

int (*getsynctime64)(struct ptp_clock_info *ptp, struct timespec64 *dev,
struct timespec64 *sys);

To simplify the PTP callback arguments (not add an additional raw
argument), it seems better to replace all of the arguments with a single
argument:

int (*getsynctime)(struct ptp_clock_info *ptp, struct correlated_ts *cts);

This requires adding a device time field to the correlated timestamp
struct:

struct correlated_ts {
          int                     (*get_ts)(struct correlated_ts *ts);
          u64                     system_ts;
          u64                     device_ts;
          ktime_t                 system_real;
          ktime_t                 system_raw;
+       ktime_t                 device;
          void                    *private;
};

The device time field is filled out by the driver "on the way back"
(following completion of get_correlated_timestamp()) to the PTP driver.

The call flow:

PTP driver-> get_synctime() (Ethernet driver)-> get_correlated_timestamp()
(Timekeeping)->get_ts (Ethernet driver)

The timestamp argument is the same (type struct correlated_ts *) for all
of these calls.

Thanks,
Chris
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