timekeeping: add CONFIG_LEGACY_TIMER_TICK

All platforms that currently do not use generic clockevents roughly call
the same set of functions in their timer interrupts: xtime_update(),
update_process_times() and profile_tick(), sometimes in a different
sequence.

Add a helper function that performs all three of them, to make the
callers more uniform and simplify the interface.

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

include/linux/timekeeping.h

@@ -12,6 +12,7 @@ extern int timekeeping_suspended;
 /* Architecture timer tick functions: */
 extern void update_process_times(int user);
 extern void xtime_update(unsigned long ticks);
+extern void legacy_timer_tick(unsigned long ticks);
 
 /*
  * Get and set timeofday

kernel/time/Kconfig

@@ -57,6 +57,13 @@ config POSIX_CPU_TIMERS_TASK_WORK
 	bool
 	default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
 
+config LEGACY_TIMER_TICK
+	bool
+	help
+	  The legacy timer tick helper is used by platforms that
+	  lack support for the generic clockevent framework.
+	  New platforms should use generic clockevents instead.
+
 if GENERIC_CLOCKEVENTS
 menu "Timers subsystem"
 

kernel/time/Makefile

@@ -16,6 +16,7 @@ ifeq ($(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST),y)
 endif
 obj-$(CONFIG_GENERIC_SCHED_CLOCK)		+= sched_clock.o
 obj-$(CONFIG_TICK_ONESHOT)			+= tick-oneshot.o tick-sched.o
+obj-$(CONFIG_LEGACY_TIMER_TICK)			+= tick-legacy.o
 obj-$(CONFIG_HAVE_GENERIC_VDSO)			+= vsyscall.o
 obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
 obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o

kernel/time/tick-legacy.c

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Timer tick function for architectures that lack generic clockevents,
+ * consolidated here from m68k/ia64/parisc/arm.
+ */
+
+#include <linux/irq.h>
+#include <linux/profile.h>
+#include <linux/timekeeper_internal.h>
+
+#include "tick-internal.h"
+
+void legacy_timer_tick(unsigned long ticks)
+{
+	if (ticks)
+		xtime_update(ticks);
+	update_process_times(user_mode(get_irq_regs()));
+	profile_tick(CPU_PROFILING);
+}