[RFC v5 0/6] Patchset enabling hardware based cross-timestamps for next gen Intel platforms

Christopher S. Hall
2016-01-04T12:45:17Z

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.

Changelog:

Changes from v4 to v5:

* Changes the history mechanism to interpolate system time using
a single historic system time pair (monotonic raw, realtime)
rather than implementing a precise history using shadow
timekeeper (see v4 changes). The advantage of this approach is
that the history can be arbitrarily long. This approach may
also be simpler in terms of coding. The major disadvantage is
that the realtime clock can be adjusted. When adjusted, the
realtime clock time (when interpolating from history) is
always approximate. In general, the longer the interpolation
period the larger the potential error. There isn't any error
interpolating the monotonic raw clock time.
* This patchset also addresses objections to the previous
patchsets overly complex correlated timestamp structure. This
patchset splits that structure into several smaller
structures. The correlated timestamp interface is renamed
cross timestamp to avoid any confusion with the correlated
clocksource.
* The correlated clocksource is separated from the cross
timestamp mechanism.
* Add monotonic raw to the PTP user interface
* Add e1000e driver configuration option that wraps Intel PCH
specific code

Changes v3 to v4:

* Adds a history mechanism to accomodate slower devices. In this
case the response time for timestamp reads to the Intel DSP
are too slow to be accomodated by the original correlated time
mechanism. The history mechanism turns shadow timekeeper into
an array where the history is stored.

Christopher S. Hall (6):
Timekeeping cross timestamp interface for device drivers
Always Running Timer (ART) correlated clocksource
Add history to cross timestamp interface supporting slower devices
Remove duplicate code from ktime_get_raw_and_real code
Add PTP_SYS_OFFSET_PRECISE for driver crosstimestamping
Adds hardware supported cross timestamp

Documentation/ptp/testptp.c | 6 +-
arch/x86/include/asm/cpufeature.h | 2 +-
arch/x86/include/asm/tsc.h | 2 +
arch/x86/kernel/tsc.c | 46 ++++++
drivers/net/ethernet/intel/Kconfig | 9 ++
drivers/net/ethernet/intel/e1000e/defines.h | 5 +
drivers/net/ethernet/intel/e1000e/ptp.c | 92 +++++++++++++++++++++++++++++
drivers/net/ethernet/intel/e1000e/regs.h | 4 +
drivers/ptp/ptp_chardev.c | 31 ++++
include/linux/clocksource.h | 43 +++++
include/linux/ptp_clock_kernel.h | 8 +
include/linux/timekeeper_internal.h | 4 +
include/linux/timekeeping.h | 42 +++++
include/uapi/linux/ptp_clock.h | 13 +-
kernel/time/timekeeping.c | 243 ++++++++++++++++++++++++++--
15 files changed, 521 insertions(+), 21 deletions(-)

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2.1.4