Merge tag 'timers-ptp-2026-06-13' of gitolite.kernel.org:pub/scm/linux/kernel/git/tip/tip

Pull timekeeping updates from Thomas Gleixner:
 "Updates for NTP/timekeeping and PTP:

   - Expand timekeeping snapshot mechanisms

     The various snapshot functions are mostly used for PTP to collect
     "atomic" snapshots of various involved clocks.

     They lack support for the recently introduced AUX clocks and do not
     provide the underlying counter value (e.g. TSC) to user space.
     Exposing the counter value snapshot allows for better control and
     steering.

     Convert the hard wired ktime_get_snapshot() to take a clock ID,
     which allows the caller to select the clock ID to be captured along
     with CLOCK_MONONOTONIC_RAW. Additionally capture the underlying
     hardware counter value and the clock source ID of the counter.

     Expand the hardware based snapshot capture where devices provide a
     mechanism to snapshot the hardware PTP clock and the system counter
     (usually via PCI/PTM) to support AUX clocks and also provide the
     captured counter value back to the caller and not only the clock
     timestamps derived from it.

   - Add a new optional read_snapshot() callback to clocksources

     That is required to capture atomic snapshots from clocksources
     which are derived from TSC with a scaling mechanism (e.g. Hyper-V,
     KVMclock).

     The value pair is handed back in the snapshot structure to the
     callers, so they can do the necessary correlations in a more
     precise way.

  This touches usage sites of the affected functions and data structure
  all over the tree, but stays fully backwards compatible for the
  existing user space exposed interfaces. New PTP IOCTLs will provide
  access to the extended functionality in later kernel versions"

* tag 'timers-ptp-2026-06-13' of gitolite.kernel.org:pub/scm/linux/kernel/git/tip/tip: (28 commits)
  ptp: vmclock: Use hw_cycles from snapshot for precise TSC pairing
  x86/kvmclock: Implement read_snapshot() for kvmclock clocksource
  clocksource/hyperv: Implement read_snapshot() for TSC page clocksource
  timekeeping: Add clocksource read_snapshot() method and hw_cycles to snapshot
  ptp: Switch to ktime_get_snapshot_id() for pre/post timestamps
  timekeeping: Add support for AUX clock cross timestamping
  timekeeping: Remove system_device_crosststamp::sys_realtime
  ALSA: hda/common: Use system_device_crosststamp::sys_systime
  wifi: iwlwifi: Use system_device_crosststamp::sys_systime
  ptp: Use system_device_crosststamp::sys_systime
  timekeeping: Prepare for cross timestamps on arbitrary clock IDs
  timekeeping: Remove ktime_get_snapshot()
  virtio_rtc: Use provided clock ID for history snapshot
  net/mlx5: Use provided clock ID for history snapshot
  igc: Use provided clock ID for history snapshot
  ice/ptp: Use provided clock ID for history snapshot
  wifi: iwlwifi: Adopt PTP cross timestamps to core changes
  timekeeping: Add CLOCK ID to system_device_crosststamp
  timekeeping: Add system_counterval_t to struct system_device_crosststamp
  timekeeping: Add CLOCK_AUX support for ktime_get_snapshot_id()
  ...

1 files changed, 24 insertions, 0 deletions

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index b12a6d19aa60..283d7297aa79 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -32,6 +32,21 @@ struct module;
 #include <vdso/clocksource.h>
 
 /**
+ * struct clocksource_hw_snapshot - Snapshot for the underlying hardware counter of derived
+ *				    clocksources like kvmclock or Hyper-V scaled TSC
+ * @hw_cycles:		The hardware counter value
+ * @hw_csid:		Clocksource ID of the hardware counter
+ *
+ * Such clocksources must implement the read_snapshot() callback and fill in the
+ * hardware counter value, the clocksource ID of the hardware counter and derive
+ * the actual clocksource cycles from @hw_cycles to provide an atomic snapshot
+ */
+struct clocksource_hw_snapshot {
+	u64			hw_cycles;
+	enum clocksource_ids	hw_csid;
+};
+
+/**
  * struct clocksource - hardware abstraction for a free running counter
  *	Provides mostly state-free accessors to the underlying hardware.
  *	This is the structure used for system time.
@@ -72,6 +87,14 @@ struct module;
  * @flags:		Flags describing special properties
  * @base:		Hardware abstraction for clock on which a clocksource
  *			is based
+ * @read_snapshot:	Extended @read() function for clocksources such as
+ *			kvmclock or the Hyper-V scaled TSC where the actual
+ *			clocksource value for timekeeping is calculated from an
+ *			underlying hardware counter. Returns the timekeeping
+ *			relevant cycle value and stores the raw value of the
+ *			underlying counter from which it was calculated
+ *			including the clocksource ID of that counter in the
+ *			clocksource hardware snapshot.
  * @enable:		Optional function to enable the clocksource
  * @disable:		Optional function to disable the clocksource
  * @suspend:		Optional suspend function for the clocksource
@@ -113,6 +136,7 @@ struct clocksource {
 	unsigned long		flags;
 	struct clocksource_base *base;
 
+	u64			(*read_snapshot)(struct clocksource *cs, struct clocksource_hw_snapshot *chs);
 	int			(*enable)(struct clocksource *cs);
 	void			(*disable)(struct clocksource *cs);
 	void			(*suspend)(struct clocksource *cs);