[tip: timers/ptp] timekeeping: Add clocksource ID to struct system_counterval_t

["tip-bot2 for Peter Hilber" <tip-bot2@linutronix.de>]

The following commit has been merged into the timers/ptp branch of tip:

Commit-ID:     93630d6df7507fa4e664110b1878c06a0c00b0b9
Gitweb:        https://git.kernel.org/tip/93630d6df7507fa4e664110b1878c06a0c00b0b9
Author:        Peter Hilber <peter.hilber@opensynergy.com>
AuthorDate:    Thu, 01 Feb 2024 02:04:47 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 07 Feb 2024 17:05:21 +01:00

timekeeping: Add clocksource ID to struct system_counterval_t

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.

Add a clocksource ID member to struct system_counterval_t, which in the
future shall identify the clocksource, and which shall replace the struct
clocksource * member. By this, get_device_system_crosststamp() callers
(such as virtio_rtc and ptp_kvm) will be able to supply easily accessible
clocksource ids instead of clocksource pointers.

[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/20240201010453.2212371-3-peter.hilber@opensynergy.com
---
 include/linux/timekeeping.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 7c43e98..ca234fa 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -273,10 +273,15 @@ struct system_device_crosststamp {
  * @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.
+ *		The default ID, CSID_GENERIC, does not identify a specific
+ *		clocksource.
  */
 struct system_counterval_t {
 	u64			cycles;
 	struct clocksource	*cs;
+	enum clocksource_ids	cs_id;
 };
 
 /*