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timekeeping: Evaluate system_counterval_t.cs_id instead of .cs

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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: Peter Hilber <peter.hilber@opensynergy.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240201010453.2212371-7-peter.hilber@opensynergy.com
This commit is contained in:
Peter Hilber 2024-02-01 02:04:51 +01:00 committed by Thomas Gleixner
parent 9be3b2f057
commit 4b7f521229
2 changed files with 10 additions and 9 deletions
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10
include/linux/timekeeping.h
View file

@ -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.
*/

9
kernel/time/timekeeping.c
View file

@ -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;