linux/clocksource.h: Extract common header for vDSO

The vDSO library should only include the necessary headers required for
a userspace library (UAPI and a minimal set of kernel headers). To make
this possible it is necessary to isolate from the kernel headers the
common parts that are strictly necessary to build the library.

Split clocksource.h into linux and common headers to make the latter
suitable for inclusion in the vDSO library.
Signed-off-by: NVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200320145351.32292-9-vincenzo.frascino@arm.com

include/linux/clocksource.h

@@ -28,16 +28,7 @@ struct module;
 #include <asm/clocksource.h>
 #endif
 
-enum vdso_clock_mode {
-	VDSO_CLOCKMODE_NONE,
-#ifdef CONFIG_GENERIC_GETTIMEOFDAY
-	VDSO_ARCH_CLOCKMODES,
-#endif
-	VDSO_CLOCKMODE_MAX,
-
-	/* Indicator for time namespace VDSO */
-	VDSO_CLOCKMODE_TIMENS = INT_MAX
-};
+#include <vdso/clocksource.h>
 
 /**
  * struct clocksource - hardware abstraction for a free running counter

include/vdso/clocksource.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_CLOCKSOURCE_H
+#define __VDSO_CLOCKSOURCE_H
+
+#include <vdso/limits.h>
+
+#if defined(CONFIG_ARCH_CLOCKSOURCE_DATA) || \
+	defined(CONFIG_GENERIC_GETTIMEOFDAY)
+#include <asm/vdso/clocksource.h>
+#endif /* CONFIG_ARCH_CLOCKSOURCE_DATA || CONFIG_GENERIC_GETTIMEOFDAY */
+
+enum vdso_clock_mode {
+	VDSO_CLOCKMODE_NONE,
+#ifdef CONFIG_GENERIC_GETTIMEOFDAY
+	VDSO_ARCH_CLOCKMODES,
+#endif
+	VDSO_CLOCKMODE_MAX,
+
+	/* Indicator for time namespace VDSO */
+	VDSO_CLOCKMODE_TIMENS = INT_MAX
+};
+
+#endif /* __VDSO_CLOCKSOURCE_H */