From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
PPS generators trigger pulses according to system time/TSC.
Timed I/O hardware understands time in ART (Always Running Timer). There
is a need to convert TSC time to ART. The conversion is done using the
detected art_to_tsc_numerator and denominator.
ART = TSC * tsc_to_art_denominator / tsc_to_art_numerator
Co-developed-by: Christopher Hall <christopher.s.hall@xxxxxxxxx>
Signed-off-by: Christopher Hall <christopher.s.hall@xxxxxxxxx>
Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
Reviewed-by: Eddie Dong <eddie.dong@xxxxxxxxx>
---
arch/x86/include/asm/tsc.h | 3 +++
arch/x86/kernel/tsc.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 594fce0ca744..f5cff8d4f61e 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -8,6 +8,8 @@
#include <asm/processor.h>
#include <asm/cpufeature.h>
+struct system_counterval_t;
+
/*
* Standard way to access the cycle counter.
*/
@@ -27,6 +29,7 @@ static inline cycles_t get_cycles(void)
}
#define get_cycles get_cycles
+extern int convert_tsc_to_art(const struct system_counterval_t *tsc, u64 *art);
extern struct system_counterval_t convert_art_to_tsc(u64 art);
extern struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 15f97c0abc9d..92b800015d8f 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -2,6 +2,7 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
+#include <linux/math.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/init.h>
@@ -1294,6 +1295,37 @@ int unsynchronized_tsc(void)
return 0;
}
+/*
+ * Converts input TSC to the corresponding ART value using conversion
+ * factors discovered by detect_art().
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int convert_tsc_to_art(const struct system_counterval_t *system_counter,
+ u64 *art)
+{
+ u64 tmp, res, rem;
+ /* ART = TSC * tsc_to_art_denominator / tsc_to_art_numerator */
+ struct u32_fract tsc_to_art = {
+ .numerator = art_to_tsc_denominator,
+ .denominator = art_to_tsc_numerator,
+ };
+
+ if (system_counter->cs != art_related_clocksource)
+ return -EINVAL;
+
+ res = system_counter->cycles - art_to_tsc_offset;
+ rem = do_div(res, tsc_to_art.denominator);
+
+ tmp = rem * tsc_to_art.numerator;
+ do_div(tmp, tsc_to_art.denominator);
+
+ *art = res * tsc_to_art.numerator + tmp;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(convert_tsc_to_art);
+
/*
* Convert ART to TSC given numerator/denominator found in detect_art()
*/
--
2.17.1
