linux-kernel - [RFC PATCH 3/4] x86/tsc: Use bool, not pointer, for ART availability

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Message-Id: <20230818011256.211078-4-peter.hilber@opensynergy.com>
Date:   Fri, 18 Aug 2023 03:12:54 +0200
From:   Peter Hilber <peter.hilber@...nsynergy.com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Hilber <peter.hilber@...nsynergy.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Marc Zyngier <maz@...nel.org>
Subject: [RFC PATCH 3/4] x86/tsc: Use bool, not pointer, for ART availability

So far, ART availability has been implicitly encoded in
art_related_clocksource, which is NULL if ART is not available.

Replace art_related_clocksource by bool have_art to explicitly indicate
ART availability.

This should reduce the changes during a tree-wide switch of struct
system_counterval_t.cs to enum clocksource_ids (when the clocksource
pointer will not be needed any more).

Signed-off-by: Peter Hilber <peter.hilber@...nsynergy.com>
---
 arch/x86/kernel/tsc.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 132045be76d0..e56cc4e97d0d 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -54,7 +54,7 @@ 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 *art_related_clocksource;
+static bool have_art;
 
 struct cyc2ns {
 	struct cyc2ns_data data[2];	/*  0 + 2*16 = 32 */
@@ -1312,8 +1312,10 @@ struct system_counterval_t convert_art_to_tsc(u64 art)
 	do_div(tmp, art_to_tsc_denominator);
 	res += tmp + art_to_tsc_offset;
 
-	return (struct system_counterval_t) {.cs = art_related_clocksource,
-			.cycles = res};
+	return (struct system_counterval_t) {
+		.cs = have_art ? &clocksource_tsc : NULL,
+		.cycles = res
+	};
 }
 EXPORT_SYMBOL(convert_art_to_tsc);
 
@@ -1350,8 +1352,10 @@ struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns)
 	do_div(tmp, USEC_PER_SEC);
 	res += tmp;
 
-	return (struct system_counterval_t) { .cs = art_related_clocksource,
-					      .cycles = res};
+	return (struct system_counterval_t) {
+		.cs = have_art ? &clocksource_tsc : NULL,
+		.cycles = res
+	};
 }
 EXPORT_SYMBOL(convert_art_ns_to_tsc);
 
@@ -1458,7 +1462,7 @@ static void tsc_refine_calibration_work(struct work_struct *work)
 		goto unreg;
 
 	if (boot_cpu_has(X86_FEATURE_ART))
-		art_related_clocksource = &clocksource_tsc;
+		have_art = true;
 	clocksource_register_khz(&clocksource_tsc, tsc_khz);
 unreg:
 	clocksource_unregister(&clocksource_tsc_early);
@@ -1484,7 +1488,7 @@ static int __init init_tsc_clocksource(void)
 	 */
 	if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) {
 		if (boot_cpu_has(X86_FEATURE_ART))
-			art_related_clocksource = &clocksource_tsc;
+			have_art = true;
 		clocksource_register_khz(&clocksource_tsc, tsc_khz);
 		clocksource_unregister(&clocksource_tsc_early);
 
-- 
2.39.2