[Intel-wired-lan] [PATCH net-next v3 1/2] e1000e: factor out systim sanitization

[Woodford, Timothy W.]

>>> This is prepatory work for an expanding list of adapter families that have occasional ~10 hour clock jumps when being used for PTP. Factor out the sanitization function and convert to using a feature (bug) flag, per suggestion from Jesse Brandeburg.
>>> 
>>> Littering functional code with device-specific checks is much messier than simply checking a flag, and having device-specific init set flags as needed.
>>> There are probably a number of other cases in the e1000e code that could/should be converted similarly.
>> 
>> Looks ok to me.
>> Adding Chris who asked what happens if we reach the max retry counter (E1000_MAX_82574_SYSTIM_REREAD)?
>> This counter is set to 50. 
>> Can you, for testing purposes, decreased this value (or even set it to 0) and see what happens?
>  I'll set the max retry counter to 1 and run an overnight test to see what happens.

After running with this configuration for about 36 hours, I haven't seen any timing jumps.  Either this configuration eliminates the error, or it makes it significantly less likely to occur.

Tim Woodford