Chris,
Basically this patch looks okay to me. Could you please add LKML,
John Stultz and tglx (the time guys) onto CC? I would like to get
their Acks or at least let them have a chance to review it.
On Thu, Jun 25, 2015 at 04:42:56PM -0700, Christopher Hall wrote:
> This patch allows system and device time ("cross-timestamp") to be performed
> by the driver. Currently, the timestamping is performed in the PTP_SYS_OFFSET
> ioctl. It reads gettimeofday() and the gettime64() callback provided by the
> driver. The cross-timestamp is best effort ignoring the latency between the
> capture of system time (getnstimeofday()) and the device time
> (driver callback).
You can make the motivation more clear by mentioning how the newer
PCIe spec foresees "perfect" timestamps. If I didn't already know the
background, I would wonder who would ever want "best effort" single
cross timestamps.
> Additionally, the callback, getsynctime64(), will only be called when
> n_samples == 1 because the driver returns only 1 cross-timestamp where
> multiple samples cannot be chained together.
There should be a way for user space to find out whether a particular
device offers the cross timestamp capability. There are reserved
fields in 'struct ptp_clock_caps' that could be used.
Thanks,
Richard
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