Commit 9094c72c authored by Anna-Maria Behnsen's avatar Anna-Maria Behnsen Committed by Thomas Gleixner
Browse files

time: Introduce auxiliary POSIX clocks 



To support auxiliary timekeeping and the related user space interfaces,
it's required to define a clock ID range for them.

Reserve 8 auxiliary clock IDs after the regular timekeeping clock ID space.

This is the maximum number of auxiliary clocks the kernel can support. The actual
number of supported clocks depends obviously on the presence of related devices
and might be constraint by the available VDSO space.

Add the corresponding timekeeper IDs as well.

Signed-off-by: default avatarAnna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarJohn Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250519083025.905800695@linutronix.de
parent f12b4586

include/linux/timekeeper_internal.h

+8 −2
Original line number Diff line number Diff line
@@ -14,10 +14,16 @@ 
/**

 * timekeeper_ids - IDs for various time keepers in the kernel

 * @TIMEKEEPER_CORE:		The central core timekeeper managing system time

 * @TIMEKEEPER_AUX_FIRST:	The first AUX timekeeper

 * @TIMEKEEPER_AUX_LAST:	The last AUX timekeeper

 * @TIMEKEEPERS_MAX:		The maximum number of timekeepers managed

 */

enum timekeeper_ids {

	TIMEKEEPER_CORE,

#ifdef CONFIG_POSIX_AUX_CLOCKS

	TIMEKEEPER_AUX_FIRST,

	TIMEKEEPER_AUX_LAST = TIMEKEEPER_AUX_FIRST + MAX_AUX_CLOCKS - 1,

#endif

	TIMEKEEPERS_MAX,

};

include/uapi/linux/time.h

+11 −0
Original line number Diff line number Diff line
@@ -64,6 +64,17 @@ struct timezone { 
#define CLOCK_TAI			11



#define MAX_CLOCKS			16



/*

 * AUX clock support. AUXiliary clocks are dynamically configured by

 * enabling a clock ID. These clock can be steered independently of the

 * core timekeeper. The kernel can support up to 8 auxiliary clocks, but

 * the actual limit depends on eventual architecture constraints vs. VDSO.

 */

#define CLOCK_AUX			MAX_CLOCKS

#define MAX_AUX_CLOCKS			8

#define CLOCK_AUX_LAST			(CLOCK_AUX + MAX_AUX_CLOCKS - 1)



#define CLOCKS_MASK			(CLOCK_REALTIME | CLOCK_MONOTONIC)

#define CLOCKS_MONO			CLOCK_MONOTONIC

kernel/time/Kconfig

+13 −2
Original line number Diff line number Diff line
@@ -82,9 +82,9 @@ config CONTEXT_TRACKING_IDLE 
	help

	  Tracks idle state on behalf of RCU.



if GENERIC_CLOCKEVENTS

menu "Timers subsystem"



if GENERIC_CLOCKEVENTS

# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is

# only related to the tick functionality. Oneshot clockevent devices

# are supported independent of this.
@@ -208,6 +208,17 @@ config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 
	  interval and NTP's maximum frequency drift of 500 parts

	  per million.	If the clocksource is good enough for NTP,

	  it is good enough for the clocksource watchdog!

endif



config POSIX_AUX_CLOCKS

	bool "Enable auxiliary POSIX clocks"

	depends on POSIX_TIMERS

	help

	  Auxiliary POSIX clocks are clocks which can be steered

	  independently of the core timekeeper, which controls the

	  MONOTONIC, REALTIME, BOOTTIME and TAI clocks.  They are useful to

	  provide e.g. lockless time accessors to independent PTP clocks

	  and other clock domains, which are not correlated to the TAI/NTP

	  notion of time.



endmenu
 
endif