clocksource: Add common vdso clock mode storage

All architectures which use the generic VDSO code have their own storage
for the VDSO clock mode. That's pointless and just requires duplicate code.

Provide generic storage for it. The new Kconfig symbol is intermediate and
will be removed once all architectures are converted over.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lkml.kernel.org/r/20200207124403.028046322@linutronix.de

kernel/time/clocksource.c

@@ -928,6 +928,15 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
 
 	clocksource_arch_init(cs);
 
+#ifdef CONFIG_GENERIC_VDSO_CLOCK_MODE
+	if (cs->vdso_clock_mode < 0 ||
+	    cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
+		pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
+			cs->name, cs->vdso_clock_mode);
+		cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
+	}
+#endif
+
 	/* Initialize mult/shift and max_idle_ns */
 	__clocksource_update_freq_scale(cs, scale, freq);
 

kernel/time/vsyscall.c

@@ -71,13 +71,19 @@ void update_vsyscall(struct timekeeper *tk)
 {
 	struct vdso_data *vdata = __arch_get_k_vdso_data();
 	struct vdso_timestamp *vdso_ts;
+	s32 clock_mode;
 	u64 nsec;
 
 	/* copy vsyscall data */
 	vdso_write_begin(vdata);
 
-	vdata[CS_HRES_COARSE].clock_mode	= __arch_get_clock_mode(tk);
-	vdata[CS_RAW].clock_mode		= __arch_get_clock_mode(tk);
+#ifdef CONFIG_GENERIC_VDSO_CLOCK_MODE
+	clock_mode = tk->tkr_mono.clock->vdso_clock_mode;
+#else
+	clock_mode = __arch_get_clock_mode(tk);
+#endif
+	vdata[CS_HRES_COARSE].clock_mode	= clock_mode;
+	vdata[CS_RAW].clock_mode		= clock_mode;
 
 	/* CLOCK_REALTIME also required for time() */
 	vdso_ts		= &vdata[CS_HRES_COARSE].basetime[CLOCK_REALTIME];