From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Christopher S. Hall" Subject: [PATCH v6 3/9] Add correlated clocksource relating aliased auxiliary and system clocks Date: Wed, 13 Jan 2016 04:12:23 -0800 Message-ID: <1452687149-11281-4-git-send-email-christopher.s.hall@intel.com> References: <1452687149-11281-1-git-send-email-christopher.s.hall@intel.com> Cc: "Christopher S. Hall" , x86@kernel.org, linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, kevin.b.stanton@intel.com To: tglx@linutronix.de, richardcochran@gmail.com, mingo@redhat.com, john.stultz@linaro.org, hpa@zytor.com, jeffrey.t.kirsher@intel.com Return-path: In-Reply-To: <1452687149-11281-1-git-send-email-christopher.s.hall@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org ACKNOWLEDGMENT: The original correlated clock source and cross timestamp code was developed by Thomas Gleixner . It has changed considerably and any mistakes are mine. The timekeeping and clocksource code don't currently comprehend two clocks that are aliases of one another. That is clocks that are *exactly* related. The correlated_cs struct encapsulated this relationship between a clocksource and its alias clock. Modern Intel hardware provides an Always Running Timer (ART) which is exactly related to TSC through a known frequency ratio. The ART is an example of a correlated clocksource. Signed-off-by: Christopher S. Hall --- include/linux/clocksource.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index 4542293..726ca68 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -267,4 +267,18 @@ struct system_counterval_t { struct clocksource *cs; }; +/* + * struct correlated_cs - Descriptor for a clocksource correlated to another + * clocksource + * @related_cs: Pointer to the related timekeeping clocksource + * @convert: Conversion function to convert a timestamp from + * the correlated clocksource to cycles of the related + * timekeeping clocksource + */ +struct correlated_cs { + struct clocksource *related_cs; + cycle_t (*convert)(struct correlated_cs *cs, + cycle_t cycles); +}; + #endif /* _LINUX_CLOCKSOURCE_H */ -- 2.1.4