[PATCH v3 3/8] 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, get_device_system_crosststamp() 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:
    v3:
    
    - Omit redundant clocksource_ids.h include (Andy Shevchenko).
    
    - Omit struct system_counterval_t member documentation, to resolve
      kernel-doc warning pointed out by Simon Horman.
    
    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           | 27 ++++++++++++++++++++-------
 include/linux/clocksource_ids.h |  2 ++
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 42328f9653c1..9f164aad5e94 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -54,6 +54,7 @@ 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 +1169,7 @@ 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 +1192,7 @@ 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 +1312,11 @@ 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);
 
@@ -1327,7 +1333,7 @@ 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
  */
 
@@ -1343,8 +1349,11 @@ 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);
 
@@ -1450,8 +1459,10 @@ 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);
@@ -1476,8 +1487,10 @@ 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