[Intel-wired-lan] [RFC PATCH] e1000e: allow non-monotonic SYSTIM readings

[Brown, Aaron F]

> From: Intel-wired-lan [mailto:intel-wired-lan-bounces at osuosl.org] On
> Behalf Of Miroslav Lichvar
> Sent: Wednesday, October 17, 2018 9:16 AM
> To: intel-wired-lan at lists.osuosl.org
> Cc: Richard Cochran <richardcochran at gmail.com>
> Subject: [Intel-wired-lan] [RFC PATCH] e1000e: allow non-monotonic SYSTIM
> readings
> 
> It seems with some NICs supported by the e1000e driver a SYSTIM reading
> may occasionally be few microseconds before the previous reading and if
> enabled also pass e1000e_sanitize_systim() without reaching the maximum
> number of rereads, even if the function is modified to check three
> consecutive readings (i.e. it doesn't look like a double read error).
> This causes an underflow in the timecounter and the PHC time jumps hours
> ahead.
> 
> This was observed on 82574, I217 and I219. The fastest way to reproduce
> it is to run a program that continuously calls the PTP_SYS_OFFSET ioctl
> on the PHC.
> 
> Modify e1000e_phc_gettime() to use timecounter_cyc2time() instead of
> timecounter_read() in order to allow non-monotonic SYSTIM readings and
> prevent the PHC from jumping.
> 
> Cc: Jacob Keller <jacob.e.keller at intel.com>
> Cc: Richard Cochran <richardcochran at gmail.com>
> Signed-off-by: Miroslav Lichvar <mlichvar at redhat.com>
> ---
>  drivers/net/ethernet/intel/e1000e/ptp.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 

Tested-by: Aaron Brown <aaron.f.brown at intel.com>