netdev - [RFC PATCH v2 1/7] timekeeping: Add clocksource ID to struct system_counterval

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Message-Id: <20231215220612.173603-2-peter.hilber@opensynergy.com>
Date: Fri, 15 Dec 2023 23:06:06 +0100
From: Peter Hilber <peter.hilber@...nsynergy.com>
To: linux-kernel@...r.kernel.org
Cc: Peter Hilber <peter.hilber@...nsynergy.com>,
	"D, Lakshmi Sowjanya" <lakshmi.sowjanya.d@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	jstultz@...gle.com,
	giometti@...eenne.com,
	corbet@....net,
	andriy.shevchenko@...ux.intel.com,
	"Dong, Eddie" <eddie.dong@...el.com>,
	"Hall, Christopher S" <christopher.s.hall@...el.com>,
	Marc Zyngier <maz@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Wanpeng Li <wanpengli@...cent.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Richard Cochran <richardcochran@...il.com>,
	kvm@...r.kernel.org,
	netdev@...r.kernel.org,
	Stephen Boyd <sboyd@...nel.org>
Subject: [RFC PATCH v2 1/7] 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 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/20230818012014.212155-1-peter.hilber@opensynergy.com/

Signed-off-by: Peter Hilber <peter.hilber@...nsynergy.com>
---

Notes:
    v2:
    
    - Refer to clocksource IDs as such in comments (Thomas Gleixner).

 include/linux/timekeeping.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index fe1e467ba046..74dc7c8b036f 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -272,10 +272,15 @@ 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;
 };
 
 /*
-- 
2.40.1