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Message-Id: <20231215220612.173603-6-peter.hilber@opensynergy.com>
Date: Fri, 15 Dec 2023 23:06:10 +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 5/7] 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 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@opensynergy.com/
Signed-off-by: Peter Hilber <peter.hilber@...nsynergy.com>
---
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
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