Re: [PATCH v6 0/9] Patchset enabling hardware based cross-timestamps for next gen Intel platforms

On Wed, Jan 13, 2016 at 4:12 AM, Christopher S. Hall
[off-list ref] wrote:

Modern Intel hardware adds an Always Running Timer (ART) that allows the
network and audio device clocks to precisely cross timestamp the device
clock with the system clock. This allows a precise correlation of the
device time and system time.

This patchset adds interfaces to the timekeeping code allowing drivers
to translate ART time to system time.

So thanks again for sending this out. Instead of sending you a bunch
of nitpicky changes as I've done in the past, I figured I'd try to
more directly help out and try to rework some of the patches to be
more to my own liking.

I've pushed them here:
   https://git.linaro.org/people/john.stultz/linux.git dev/xtimestamp

My main changes have been:
* Reordered the patches, putting all the timekeeping core changes
first, then the usage of those interfaces last.

* Implemented Richard's suggestion to drop one of the helper
structures that didn't provide much value

* Moved structures defined in clocksource.h but only used in
timekeeping.h to timekeeping.h

* Fixed a few build issues I caught (as well as some of the ones
kbuild bot found)

* Reworked the tsc logic to avoid 64bit divisions (which don't build
on 32bit systems)

I still have not:
* Done *any* testing at all with this. Please verify I didn't break anything. :)

* Fixed the 64bit div on 32bit systems build issue in
get_device_system_crosststamp()/adjust_historical_crosststamp()

* Done another review/edit pass on the commit messages, as they've
gotten a bit long (I know, I know.. "be verbose" I said!), but they
can probably be tweaked to be better and more contextual to the
patches.

Still on the fence:
* Probably should zap the correlated_cs structure or move it to tsc.h,
as mentioned in my other email

Anyway, I'll let you take a look at this and feel free to integrate
and adapt these ideas as you please into your patchset. Look forward
to your next revision!

thanks
-john