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 it will be dropped from struct system_counterval_t in the future. By this, get_device_system_crosststamp() callers (such as virtio_rtc and ptp_kvm) will no longer need to supply clocksource pointers. This change should not alter any behavior, as the struct system_counterval_t clocksource ID is already being set wherever the clocksource pointer is set. get_device_system_crosststamp() will now fail if the clocksource has id CSID_GENERIC, but all currently relevant clocksources have a custom clocksource id. [1] https://lore.kernel.org/lkml/20230818012014.212155-1-peter.hilber@xxxxxxxxxxxxxxx/ Signed-off-by: Peter Hilber <peter.hilber@xxxxxxxxxxxxxxx> --- Notes: v2: - Refer to clocksource IDs as such in comments (Thomas Gleixner). - Update comments which were still referring to clocksource pointers. include/linux/timekeeping.h | 10 +++++----- kernel/time/timekeeping.c | 9 +++++---- 2 files changed, 10 insertions(+), 9 deletions(-) diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 74dc7c8b036f..75e957171bd5 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -267,13 +267,13 @@ 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. */ diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 266d02809dbb..0ff065c5d25b 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -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; -- 2.40.1
