Commit 4b7f5212 authored by Peter Hilber's avatar Peter Hilber Committed by Thomas Gleixner
Browse files

timekeeping: Evaluate system_counterval_t.cs_id instead of .cs 

Clocksource pointers can be problematic to obtain for drivers which are not
clocksource drivers themselves. In particular, the RFC virtio_rtc driver
[1] would require a new helper function to obtain a pointer to the ARM
Generic Timer clocksource. The ptp_kvm driver also required a similar
workaround.

Address this by evaluating the clocksource ID, rather than the clocksource
pointer, of struct system_counterval_t. By this, setting the clocksource
pointer becomes unneeded, and get_device_system_crosststamp() callers will
no longer need to supply clocksource pointers.

All relevant clocksource drivers provide the ID, so this change is not
changing the behaviour.

[1] https://lore.kernel.org/lkml/20231218073849.35294-1-peter.hilber@opensynergy.com/



Signed-off-by: default avatarPeter Hilber <peter.hilber@opensynergy.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240201010453.2212371-7-peter.hilber@opensynergy.com
parent 9be3b2f0

include/linux/timekeeping.h

+5 −5
Original line number Diff line number Diff line
@@ -268,13 +268,13 @@ struct system_device_crosststamp { 
};



/**

 * struct system_counterval_t - system counter value with the pointer to the

 * struct system_counterval_t - system counter value with the ID of the

 *				corresponding clocksource

 * @cycles:	System counter value

 * @cs:		Clocksource corresponding to system counter value. Used by

 *		timekeeping code to verify comparibility of two cycle values

 * @cs_id:	Clocksource ID corresponding to system counter value. To be

 *		used instead of cs in the future.

 * @cs:		Clocksource corresponding to system counter value. Timekeeping

 *		code now evaluates cs_id instead.

 * @cs_id:	Clocksource ID corresponding to system counter value. Used by

 *		timekeeping code to verify comparability of two cycle values.

 *		The default ID, CSID_GENERIC, does not identify a specific

 *		clocksource.

 */

kernel/time/timekeeping.c

+5 −4
Original line number Diff line number Diff line
@@ -1232,11 +1232,12 @@ int get_device_system_crosststamp(int (*get_time_fn) 
			return ret;



		/*

		 * Verify that the clocksource associated with the captured

		 * system counter value is the same as the currently installed

		 * timekeeper clocksource

		 * Verify that the clocksource ID associated with the captured

		 * system counter value is the same as for the currently

		 * installed timekeeper clocksource

		 */

		if (tk->tkr_mono.clock != system_counterval.cs)

		if (system_counterval.cs_id == CSID_GENERIC ||

		    tk->tkr_mono.clock->id != system_counterval.cs_id)

			return -ENODEV;

		cycles = system_counterval.cycles;