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

["Woodford, Timothy W." <Timothy.Woodford@jhuapl.edu>]

>> 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 have one of the affected NICs.  I inserted some test code into the module to check the value of i after the for loop inside the sanitize function exits to check how many iterations of the loop were being run.  I ran a PTP test setup for a few hours with E1000_MAX_82574_SYSTIM_REREAD=50, and the maximum number was 5 iterations.
It looks like setting E1000_MAX_82574_SYSTIM_REREAD to 0 will just disable the return value checking and will have the same results as disabling the sanitization function.  I'll set the max retry counter to 1 and run an overnight test to see what happens.

Tim Woodford