On 08/07/2015 04:01 PM, Christopher Hall wrote:
Original patch description:
Subject: ptp: Get sync timestamps
From: Thomas Gleixner <t...@linutronix.de>
Date: Wed, 29 Jul 2015 10:52:06 +0200
The ART stuff wants to be splitted out.
======== Changes =======
Add struct correlated_cs (clocksource) with pointer to original clocksource
and function pointer to convert correlated clocksource to the original
Add struct correlated_ts (timestamp) with function pointer to read correlated
clocksource, device and system (in terms of correlated clocksource)
counter values (input) with resulting converted real and monotonic raw
system times (output)
Add get_correlated_timestamp() function which given specific correlated_cs
and correlated_ts convert correlated counter value to system time
Add art_to_tsc conversion function translated Always Running Timer (ART) to
TSC value
---
arch/x86/kernel/tsc.c | 31 ++++++++++++++++++++++
include/linux/clocksource.h | 30 +++++++++++++++++++++
include/linux/timekeeping.h | 4 +++
kernel/time/timekeeping.c | 63 +++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 128 insertions(+)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 7437b41..a90aa6a 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1059,6 +1059,27 @@ int unsynchronized_tsc(void)
return 0;
}
+static u32 tsc_numerator;
+static u32 tsc_denominator;
+/*
+ * CHECKME: Do we need the adjust value? It should be 0, but if we run
+ * in a VM this might be a different story.
+ */
+static u64 tsc_adjust;
+
+static u64 art_to_tsc(u64 cycles)
+{
+ u64 tmp, res = tsc_adjust;
+
+ res += (cycles / tsc_denominator) * tsc_numerator;
+ tmp = (cycles % tsc_denominator) * tsc_numerator;
+ res += tmp / tsc_denominator;
+ return res;
Nice trick!
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 278dd27..2ed3d0c 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -258,4 +258,34 @@ void acpi_generic_timer_init(void);
static inline void acpi_generic_timer_init(void) { }
#endif
+/**
+ * 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;
+ u64 (*convert)(u64 cycles);
Should the name make it clearer which way it converts? For example,
convert_to_related? We might also want convert_from_related.
--Andy
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