x86/tsc: Convert ART in nanoseconds to TSC (fc804f65) · Commits · 戴 / test

Device drivers use get_device_system_crosststamp() to produce precise system/device cross-timestamps. The PHC clock and ALSA interfaces, for example, make the cross-timestamps available to user applications. On Intel platforms, get_device_system_crosststamp() requires a TSC value derived from ART (Always Running Timer) to compute the monotonic raw and realtime system timestamps. Starting with Intel Goldmont platforms, the PCIe root complex supports the PTM time sync protocol. PTM requires all timestamps to be in units of nanoseconds. The Intel root complex hardware propagates system time derived from ART in units of nanoseconds performing the conversion as follows: ART_NS = ART * 1e9 / <crystal frequency> When user software requests a cross-timestamp, the system timestamps (generally read from device registers) must be converted to TSC by the driver software as follows: TSC = ART_NS * TSC_KHZ / 1e6 This is valid when CPU feature flag X86_FEATURE_TSC_KNOWN_FREQ is set indicating that tsc_khz is derived from CPUID[15H]. Drivers should check whether this flag is set before conversion to TSC is attempted. Suggested-by:

Christopher S. Hall <christopher.s.hall@intel.com> Signed-off-by:

Rajvi Jingar <rajvi.jingar@intel.com> Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Cc: peterz@infradead.org Link: https://lkml.kernel.org/r/1520530116-4925-1-git-send-email-rajvi.jingar@intel.com

arch/x86/include/asm/tsc.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -31,6 +31,7 @@ static inline cycles_t get_cycles(void)
		}

		extern struct system_counterval_t convert_art_to_tsc(u64 art);
		extern struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns);

		extern void tsc_early_delay_calibrate(void);
		extern void tsc_init(void);

arch/x86/kernel/tsc.c

+39 −0

Original line number	Diff line number	Diff line
		@@ -1179,6 +1179,45 @@ struct system_counterval_t convert_art_to_tsc(u64 art)
		}
		EXPORT_SYMBOL(convert_art_to_tsc);

		/**
		* convert_art_ns_to_tsc() - Convert ART in nanoseconds to TSC.
		* @art_ns: ART (Always Running Timer) in unit of nanoseconds
		*
		* PTM requires all timestamps to be in units of nanoseconds. When user
		* software requests a cross-timestamp, this function converts system timestamp
		* to TSC.
		*
		* This is valid when CPU feature flag X86_FEATURE_TSC_KNOWN_FREQ is set
		* indicating the tsc_khz is derived from CPUID[15H]. Drivers should check
		* that this flag is set before conversion to TSC is attempted.
		*
		* Return:
		* struct system_counterval_t - system counter value with the pointer to 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.
		*/

		struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns)
		{
		u64 tmp, res, rem;

		rem = do_div(art_ns, USEC_PER_SEC);

		res = art_ns * tsc_khz;
		tmp = rem * tsc_khz;

		do_div(tmp, USEC_PER_SEC);
		res += tmp;

		return (struct system_counterval_t) { .cs = art_related_clocksource,
		.cycles = res};
		}
		EXPORT_SYMBOL(convert_art_ns_to_tsc);


		static void tsc_refine_calibration_work(struct work_struct *work);
		static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work);
		/**

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