all platforms: separate cpu_initclocks() from cpu_startclock()

To give the primary CPU an opportunity to perform clock interrupt
preparation in a machine-independent manner we need to separate the
"initialization" parts of cpu_initclocks() from the "start the clock
interrupt" parts.  Currently, cpu_initclocks() does everything all at
once, so there is no space for this MI setup.

Many platforms have more-or-less already done this separation by
implementing a separate routine named "cpu_startclock()".  This patch
promotes cpu_startclock() from de facto standard to mandatory API.

- Prototype cpu_startclock() in sys/systm.h alongside cpu_initclocks().
  The separation of responsibility between the two routines is a bit
  fuzzy but the basic guidelines are as follows:

  + cpu_initclocks() must initialize hz, stathz, and profhz, and call
    clockintr_init().

  + cpu_startclock() must call clockintr_cpu_init() and start the clock
    interrupt cycle on the calling CPU.

  These guidelines will shift in the future, but that's the way things
  stand as of *this* commit.

- In initclocks(): first call cpu_initclocks(), then do MI setup, and
  last call cpu_startclock().

- On platforms where cpu_startclock() already exists: don't call
  cpu_startclock() from cpu_initclocks() anymore.

- On platforms where cpu_startclock() doesn't yet exist: implement it.
  Usually this is as simple as dividing cpu_initclocks() in two.

Tested on amd64 (i8254, lapic), arm64, i386 (i8254, lapic), macppc,
mips64/octeon, and sparc64.  Tested on arm/armv7 (agtimer(4)) by
phessler@ and jmatthew@.  Tested on m88k/luna88k by aoyama@.  Tested
on powerpc64 by gkoehler@ and mlarkin@.  Tested on riscv64 by
jmatthew@.

Thread: https://marc.info/?l=openbsd-tech&m=169195251322149&w=2

4 files changed, 20 insertions, 7 deletions

diff --git a/sys/arch/i386/i386/lapic.c b/sys/arch/i386/i386/lapic.c
index fae8f71cbfc..49d9dfcfe89 100644
--- a/sys/arch/i386/i386/lapic.c
+++ b/sys/arch/i386/i386/lapic.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: lapic.c,v 1.55 2023/02/09 01:41:15 cheloha Exp $	*/
+/*	$OpenBSD: lapic.c,v 1.56 2023/08/23 01:55:46 cheloha Exp $	*/
 /* $NetBSD: lapic.c,v 1.1.2.8 2000/02/23 06:10:50 sommerfeld Exp $ */
 
 /*-
@@ -327,8 +327,6 @@ lapic_initclocks(void)
 	stathz = hz;
 	profhz = stathz * 10;
 	clockintr_init(CL_RNDSTAT);
-
-	lapic_startclock();
 }
 
 extern int gettick(void);	/* XXX put in header file */
@@ -422,6 +420,7 @@ lapic_calibrate_timer(struct cpu_info *ci)
 	    lapic_per_second * (1ULL << 32) / 1000000000;
 	lapic_timer_nsec_max = UINT64_MAX / lapic_timer_nsec_cycle_ratio;
 	initclock_func = lapic_initclocks;
+	startclock_func = lapic_startclock;
 }
 
 /*
diff --git a/sys/arch/i386/i386/machdep.c b/sys/arch/i386/i386/machdep.c
index 9ce08823da5..2599def386c 100644
--- a/sys/arch/i386/i386/machdep.c
+++ b/sys/arch/i386/i386/machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: machdep.c,v 1.668 2023/08/16 09:51:39 jsg Exp $	*/
+/*	$OpenBSD: machdep.c,v 1.669 2023/08/23 01:55:46 cheloha Exp $	*/
 /*	$NetBSD: machdep.c,v 1.214 1996/11/10 03:16:17 thorpej Exp $	*/
 
 /*-
@@ -233,6 +233,7 @@ void (*cpusensors_setup)(struct cpu_info *);
 
 void (*delay_func)(int) = i8254_delay;
 void (*initclock_func)(void) = i8254_initclocks;
+void (*startclock_func)(void) = i8254_start_both_clocks;
 
 /*
  * Extent maps to manage I/O and ISA memory hole space.  Allocate
@@ -3439,6 +3440,12 @@ cpu_initclocks(void)
 }
 
 void
+cpu_startclock(void)
+{
+	(*startclock_func)();
+}
+
+void
 need_resched(struct cpu_info *ci)
 {
 	ci->ci_want_resched = 1;
diff --git a/sys/arch/i386/include/cpu.h b/sys/arch/i386/include/cpu.h
index 2496ba30140..297344bace9 100644
--- a/sys/arch/i386/include/cpu.h
+++ b/sys/arch/i386/include/cpu.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cpu.h,v 1.182 2023/07/25 18:16:20 cheloha Exp $	*/
+/*	$OpenBSD: cpu.h,v 1.183 2023/08/23 01:55:46 cheloha Exp $	*/
 /*	$NetBSD: cpu.h,v 1.35 1996/05/05 19:29:26 christos Exp $	*/
 
 /*-
@@ -399,6 +399,9 @@ extern int i386_has_sse2;
 
 extern void (*update_cpuspeed)(void);
 
+extern void (*initclock_func)(void);
+extern void (*startclock_func)(void);
+
 /* machdep.c */
 void	dumpconf(void);
 void	cpu_reset(void);
@@ -416,7 +419,6 @@ void	switch_exit(struct proc *);
 void	proc_trampoline(void);
 
 /* clock.c */
-extern void (*initclock_func)(void);
 void	startclocks(void);
 void	rtcinit(void);
 void	rtcstart(void);
@@ -424,6 +426,7 @@ void	rtcstop(void);
 void	i8254_delay(int);
 void	i8254_initclocks(void);
 void	i8254_startclock(void);
+void	i8254_start_both_clocks(void);
 void	i8254_inittimecounter(void);
 void	i8254_inittimecounter_simple(void);
 
diff --git a/sys/arch/i386/isa/clock.c b/sys/arch/i386/isa/clock.c
index 563feaabf99..630be7642a2 100644
--- a/sys/arch/i386/isa/clock.c
+++ b/sys/arch/i386/isa/clock.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: clock.c,v 1.66 2023/08/22 17:13:22 cheloha Exp $	*/
+/*	$OpenBSD: clock.c,v 1.67 2023/08/23 01:55:46 cheloha Exp $	*/
 /*	$NetBSD: clock.c,v 1.39 1996/05/12 23:11:54 mycroft Exp $	*/
 
 /*-
@@ -427,7 +427,11 @@ i8254_initclocks(void)
 	stathz = 128;
 	profhz = 1024;		/* XXX does not divide into 1 billion */
 	clockintr_init(0);
+}
 
+void
+i8254_start_both_clocks(void)
+{
 	clockintr_cpu_init(NULL);
 
 	/*