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From: lakshmi.sowjanya.d@intel.com
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Subject: [RFC PATCH v2 01/10] x86/tsc: Add base clock properties in clocksource structure
Date: Thu, 21 Dec 2023 15:02:45 +0530
Message-Id: <20231221093254.9599-2-lakshmi.sowjanya.d@intel.com>
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From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@intel.com>

Remove convert_art_to_tsc() and convert_art_ns_to_tsc(), as this patch
series introduces a generic function ktime_real_to_base_clock() to
convert realtime to base clock domain.

Add hardware abstraction, struct clocksource_base in clocksource.

Add clocksource ID for x86 ART(Always Running Timer).

Co-developed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Co-developed-by: Christopher S. Hall <christopher.s.hall@intel.com>
Signed-off-by: Christopher S. Hall <christopher.s.hall@intel.com>
Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@intel.com>
---
 arch/x86/include/asm/tsc.h      |  3 --
 arch/x86/kernel/tsc.c           | 94 +++++++--------------------------
 include/linux/clocksource.h     | 27 ++++++++++
 include/linux/clocksource_ids.h |  1 +
 4 files changed, 47 insertions(+), 78 deletions(-)

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 594fce0ca744..5e36495cc821 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -27,9 +27,6 @@ static inline cycles_t get_cycles(void)
 }
 #define get_cycles get_cycles
 
-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_init(void);
 extern void tsc_init(void);
 extern void mark_tsc_unstable(char *reason);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 868f09966b0f..b45ce594cfef 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -51,9 +51,9 @@ int tsc_clocksource_reliable;
 
 static int __read_mostly tsc_force_recalibrate;
 
-static u32 art_to_tsc_numerator;
-static u32 art_to_tsc_denominator;
-static u64 art_to_tsc_offset;
+static struct clocksource_base art_base_clk = {
+	.id    = CSID_X86_ART,
+};
 static bool have_art;
 
 struct cyc2ns {
@@ -1075,7 +1075,7 @@ core_initcall(cpufreq_register_tsc_scaling);
  */
 static void __init detect_art(void)
 {
-	unsigned int unused[2];
+	unsigned int unused;
 
 	if (boot_cpu_data.cpuid_level < ART_CPUID_LEAF)
 		return;
@@ -1090,13 +1090,14 @@ static void __init detect_art(void)
 	    tsc_async_resets)
 		return;
 
-	cpuid(ART_CPUID_LEAF, &art_to_tsc_denominator,
-	      &art_to_tsc_numerator, unused, unused+1);
+	cpuid(ART_CPUID_LEAF, &art_base_clk.denominator,
+		&art_base_clk.numerator, &art_base_clk.freq_khz, &unused);
 
-	if (art_to_tsc_denominator < ART_MIN_DENOMINATOR)
+	art_base_clk.freq_khz /= KHZ;
+	if (art_base_clk.denominator < ART_MIN_DENOMINATOR)
 		return;
 
-	rdmsrl(MSR_IA32_TSC_ADJUST, art_to_tsc_offset);
+	rdmsrl(MSR_IA32_TSC_ADJUST, art_base_clk.offset);
 
 	/* Make this sticky over multiple CPU init calls */
 	setup_force_cpu_cap(X86_FEATURE_ART);
@@ -1297,69 +1298,6 @@ int unsynchronized_tsc(void)
 	return 0;
 }
 
-/*
- * Convert ART to TSC given numerator/denominator found in detect_art()
- */
-struct system_counterval_t convert_art_to_tsc(u64 art)
-{
-	u64 tmp, res, rem;
-
-	rem = do_div(art, art_to_tsc_denominator);
-
-	res = art * art_to_tsc_numerator;
-	tmp = rem * art_to_tsc_numerator;
-
-	do_div(tmp, art_to_tsc_denominator);
-	res += tmp + art_to_tsc_offset;
-
-	return (struct system_counterval_t) {
-		.cs_id = have_art ? CSID_X86_TSC : CSID_GENERIC,
-		.cycles = res
-	};
-}
-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 ID of the
- *	corresponding clocksource
- *	@cycles:	System counter value
- *	@cs_id:		Clocksource ID corresponding to system counter value.
- *			Used by timekeeping code to verify comparability 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_id = have_art ? CSID_X86_TSC : CSID_GENERIC,
-		.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);
 /**
@@ -1461,8 +1399,10 @@ static void tsc_refine_calibration_work(struct work_struct *work)
 	if (tsc_unstable)
 		goto unreg;
 
-	if (boot_cpu_has(X86_FEATURE_ART))
+	if (boot_cpu_has(X86_FEATURE_ART)) {
 		have_art = true;
+		clocksource_tsc.base = &art_base_clk;
+	}
 	clocksource_register_khz(&clocksource_tsc, tsc_khz);
 unreg:
 	clocksource_unregister(&clocksource_tsc_early);
@@ -1487,8 +1427,10 @@ static int __init init_tsc_clocksource(void)
 	 * the refined calibration and directly register it as a clocksource.
 	 */
 	if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) {
-		if (boot_cpu_has(X86_FEATURE_ART))
+		if (boot_cpu_has(X86_FEATURE_ART)) {
 			have_art = true;
+			clocksource_tsc.base = &art_base_clk;
+		}
 		clocksource_register_khz(&clocksource_tsc, tsc_khz);
 		clocksource_unregister(&clocksource_tsc_early);
 
@@ -1512,10 +1454,12 @@ static bool __init determine_cpu_tsc_frequencies(bool early)
 
 	if (early) {
 		cpu_khz = x86_platform.calibrate_cpu();
-		if (tsc_early_khz)
+		if (tsc_early_khz) {
 			tsc_khz = tsc_early_khz;
-		else
+		} else {
 			tsc_khz = x86_platform.calibrate_tsc();
+			clocksource_tsc.freq_khz = tsc_khz;
+		}
 	} else {
 		/* We should not be here with non-native cpu calibration */
 		WARN_ON(x86_platform.calibrate_cpu != native_calibrate_cpu);
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 1d42d4b17327..0a1110a0e660 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -21,6 +21,7 @@
 #include <asm/div64.h>
 #include <asm/io.h>
 
+struct clocksource_base;
 struct clocksource;
 struct module;
 
@@ -48,6 +49,7 @@ struct module;
  * @archdata:		Optional arch-specific data
  * @max_cycles:		Maximum safe cycle value which won't overflow on
  *			multiplication
+ * @freq_khz:		Clocksource frequency in khz.
  * @name:		Pointer to clocksource name
  * @list:		List head for registration (internal)
  * @rating:		Rating value for selection (higher is better)
@@ -70,6 +72,8 @@ struct module;
  *			validate the clocksource from which the snapshot was
  *			taken.
  * @flags:		Flags describing special properties
+ * @base:		Hardware abstraction for clock on which a clocksource
+ *			is based
  * @enable:		Optional function to enable the clocksource
  * @disable:		Optional function to disable the clocksource
  * @suspend:		Optional suspend function for the clocksource
@@ -105,12 +109,14 @@ struct clocksource {
 	struct arch_clocksource_data archdata;
 #endif
 	u64			max_cycles;
+	u32			freq_khz;
 	const char		*name;
 	struct list_head	list;
 	int			rating;
 	enum clocksource_ids	id;
 	enum vdso_clock_mode	vdso_clock_mode;
 	unsigned long		flags;
+	struct clocksource_base *base;
 
 	int			(*enable)(struct clocksource *cs);
 	void			(*disable)(struct clocksource *cs);
@@ -294,4 +300,25 @@ static inline void timer_probe(void) {}
 extern ulong max_cswd_read_retries;
 void clocksource_verify_percpu(struct clocksource *cs);
 
+/**
+ * struct clocksource_base - hardware abstraction for clock on which a clocksource
+ *			is based
+ * @id:			Defaults to CSID_GENERIC. The id value is used for conversion
+ *			functions which require that the current clocksource is based
+ *			on a clocksource_base with a particular ID in certain snapshot
+ *			functions to allow callers to validate the clocksource from
+ *			which the snapshot was taken.
+ * @freq_khz:		Nominal frequency of the base clock in kHz
+ * @offset:		Offset between the base clock and the clocksource
+ * @numerator:		Numerator of the clock ratio between base clock and the clocksource
+ * @denominator:	Denominator of the clock ratio between base clock and the clocksource
+ */
+struct clocksource_base {
+	enum clocksource_ids	id;
+	u32			freq_khz;
+	u64			offset;
+	u32			numerator;
+	u32			denominator;
+};
+
 #endif /* _LINUX_CLOCKSOURCE_H */
diff --git a/include/linux/clocksource_ids.h b/include/linux/clocksource_ids.h
index a4fa3436940c..2bb4d8c2f1b0 100644
--- a/include/linux/clocksource_ids.h
+++ b/include/linux/clocksource_ids.h
@@ -9,6 +9,7 @@ enum clocksource_ids {
 	CSID_X86_TSC_EARLY,
 	CSID_X86_TSC,
 	CSID_X86_KVM_CLK,
+	CSID_X86_ART,
 	CSID_MAX,
 };
 
-- 
2.35.3