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    Subject[PATCH v8 0/8] Patchset enabling hardware based cross-timestamps for next gen Intel platforms
    Date
    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 v7 to v8:

    * Fix comments in timekeeping.c
    * Re-use older TSC feature, removing "invariant" TSC in ART
    detection code

    Changes from v6 to v7:

    * Reorder several patches
    * Removed correlated clocksource
    * Fixed 32-bit compile issues
    * Added multiplication overflow detection to history computation
    * Added invariant tsc CPU feature - this is related to ART, but
    is a separate feature


    Changes from v5 to v6:

    * Pulled supporting code for snapshotting, correlated
    clocksource, and cycles to nanoseconds translation to separate
    patches. Added patches are marked as NEW below. There is,
    however, very little *actually* new code, just reorganized
    code
    * Renamed and moved clocksource change sequence to timekeeper
    struct (out of tk_read_base)
    * Renamed structs for system counter and synced device time
    callback to system_counterval_t and sync_device_time_cb,
    respectively
    * Changed PTP cross-timestamp callback name to getcrosststamp
    for consistency with the timekeeping code - corresponding
    function name changes in e1000e driver
    * Simplified PTP time calculations making use of ktime_to_* code

    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 (8):
    time: Add cycles to nanoseconds translation
    time: Add timekeeping snapshot code capturing system time and counter
    time: Remove duplicated code in ktime_get_raw_and_real()
    time: Add driver cross timestamp interface for higher precision time
    synchronization
    time: Add history to cross timestamp interface supporting slower
    devices
    x86: tsc: Always Running Timer (ART) correlated clocksource
    ptp: Add PTP_SYS_OFFSET_PRECISE for driver crosstimestamping
    net: e1000e: Adds hardware supported cross timestamp on e1000e nic

    Documentation/ptp/testptp.c | 6 +-
    arch/x86/include/asm/cpufeature.h | 2 +-
    arch/x86/include/asm/tsc.h | 2 +
    arch/x86/kernel/tsc.c | 49 +++++
    drivers/net/ethernet/intel/Kconfig | 9 +
    drivers/net/ethernet/intel/e1000e/defines.h | 5 +
    drivers/net/ethernet/intel/e1000e/ptp.c | 85 ++++++++
    drivers/net/ethernet/intel/e1000e/regs.h | 4 +
    drivers/ptp/ptp_chardev.c | 27 +++
    include/linux/pps_kernel.h | 17 +-
    include/linux/ptp_clock_kernel.h | 8 +
    include/linux/timekeeper_internal.h | 2 +
    include/linux/timekeeping.h | 58 ++++++
    include/uapi/linux/ptp_clock.h | 13 +-
    kernel/time/timekeeping.c | 290 +++++++++++++++++++++++++---
    15 files changed, 537 insertions(+), 40 deletions(-)

    --
    2.1.4

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