[RFC PATCH v2 2/7] x86/tsc: Add clocksource ID, set system_counterval_t.cs_id

[Peter Hilber]

Add a clocksource ID for TSC and a distinct one for the early TSC.

Use distinct IDs for TSC and early TSC, since those also have distinct
clocksource structs. This should help to keep existing semantics when
comparing clocksources.

Also, set the recently added struct system_counterval_t member cs_id to the
TSC ID in the cases where the clocksource member is being set to the TSC
clocksource. In the future, this will keep get_device_system_crosststamp()
working, when it will compare the clocksource id in struct
system_counterval_t, rather than the clocksource.

For the x86 ART related code, system_counterval_t.cs == NULL corresponds to
system_counterval_t.cs_id == CSID_GENERIC (0).

Signed-off-by: Peter Hilber <peter.hilber@xxxxxxxxxxxxxxx>
---

Notes:
    v2:
    
    - Name clock id according to Thomas Gleixner's mockup.
    
    - Refer to clocksource IDs as such in comments (Thomas Gleixner).
    
    - Update comments which were still referring to clocksource pointers.

 arch/x86/kernel/tsc.c           | 31 ++++++++++++++++++++++++-------
 include/linux/clocksource_ids.h |  2 ++
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 15f97c0abc9d..9367174f7920 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -11,6 +11,7 @@
 #include <linux/cpufreq.h>
 #include <linux/delay.h>
 #include <linux/clocksource.h>
+#include <linux/clocksource_ids.h>
 #include <linux/percpu.h>
 #include <linux/timex.h>
 #include <linux/static_key.h>
@@ -54,6 +55,7 @@ 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 */
@@ -1168,6 +1170,7 @@ static struct clocksource clocksource_tsc_early = {
 	.mask			= CLOCKSOURCE_MASK(64),
 	.flags			= CLOCK_SOURCE_IS_CONTINUOUS |
 				  CLOCK_SOURCE_MUST_VERIFY,
+	.id			= CSID_X86_TSC_EARLY,
 	.vdso_clock_mode	= VDSO_CLOCKMODE_TSC,
 	.enable			= tsc_cs_enable,
 	.resume			= tsc_resume,
@@ -1190,6 +1193,7 @@ static struct clocksource clocksource_tsc = {
 				  CLOCK_SOURCE_VALID_FOR_HRES |
 				  CLOCK_SOURCE_MUST_VERIFY |
 				  CLOCK_SOURCE_VERIFY_PERCPU,
+	.id			= CSID_X86_TSC,
 	.vdso_clock_mode	= VDSO_CLOCKMODE_TSC,
 	.enable			= tsc_cs_enable,
 	.resume			= tsc_resume,
@@ -1309,8 +1313,11 @@ 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 = art_related_clocksource,
+		.cs_id = have_art ? CSID_X86_TSC : CSID_GENERIC,
+		.cycles = res
+	};
 }
 EXPORT_SYMBOL(convert_art_to_tsc);
 
@@ -1327,12 +1334,15 @@ EXPORT_SYMBOL(convert_art_to_tsc);
  * that this flag is set before conversion to TSC is attempted.
  *
  * Return:
- * struct system_counterval_t - system counter value with the pointer to the
+ * struct system_counterval_t - system counter value with the ID of the
  *	corresponding clocksource
  *	@cycles:	System counter value
  *	@cs:		Clocksource corresponding to system counter value. Used
  *			by timekeeping code to verify comparability of two cycle
  *			values.
+ *	@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)
@@ -1347,8 +1357,11 @@ 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 = art_related_clocksource,
+		.cs_id = have_art ? CSID_X86_TSC : CSID_GENERIC,
+		.cycles = res
+	};
 }
 EXPORT_SYMBOL(convert_art_ns_to_tsc);
 
@@ -1454,8 +1467,10 @@ 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)) {
 		art_related_clocksource = &clocksource_tsc;
+		have_art = true;
+	}
 	clocksource_register_khz(&clocksource_tsc, tsc_khz);
 unreg:
 	clocksource_unregister(&clocksource_tsc_early);
@@ -1480,8 +1495,10 @@ 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)) {
 			art_related_clocksource = &clocksource_tsc;
+			have_art = true;
+		}
 		clocksource_register_khz(&clocksource_tsc, tsc_khz);
 		clocksource_unregister(&clocksource_tsc_early);
 
diff --git a/include/linux/clocksource_ids.h b/include/linux/clocksource_ids.h
index 16775d7d8f8d..f8467946e9ee 100644
--- a/include/linux/clocksource_ids.h
+++ b/include/linux/clocksource_ids.h
@@ -6,6 +6,8 @@
 enum clocksource_ids {
 	CSID_GENERIC		= 0,
 	CSID_ARM_ARCH_COUNTER,
+	CSID_X86_TSC_EARLY,
+	CSID_X86_TSC,
 	CSID_MAX,
 };
 
-- 
2.40.1