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

From: Christopher Hall
Date: Fri Nov 06 2015 - 21:16:05 EST


On Tue, 13 Oct 2015 06:59:26 -0700, Richard Cochran <richardcochran@xxxxxxxxx> 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

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

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

This requires adding a device time field to the correlated timestamp

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.

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