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, 19 insertions, 7 deletions

diff --git a/sys/arch/amd64/amd64/lapic.c b/sys/arch/amd64/amd64/lapic.c
index da17b0875f7..4e7182ecb5e 100644
--- a/sys/arch/amd64/amd64/lapic.c
+++ b/sys/arch/amd64/amd64/lapic.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: lapic.c,v 1.68 2023/04/26 10:52:55 mlarkin Exp $	*/
+/*	$OpenBSD: lapic.c,v 1.69 2023/08/23 01:55:46 cheloha Exp $	*/
 /* $NetBSD: lapic.c,v 1.2 2003/05/08 01:04:35 fvdl Exp $ */
 
 /*-
@@ -499,8 +499,6 @@ lapic_initclocks(void)
 	stathz = hz;
 	profhz = stathz * 10;
 	clockintr_init(CL_RNDSTAT);
-
-	lapic_startclock();
 }
 
 
@@ -599,6 +597,7 @@ skip_calibration:
 	    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/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index 453de13fbfb..8c5f398b88c 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: machdep.c,v 1.286 2023/07/27 00:28:25 guenther Exp $	*/
+/*	$OpenBSD: machdep.c,v 1.287 2023/08/23 01:55:45 cheloha Exp $	*/
 /*	$NetBSD: machdep.c,v 1.3 2003/05/07 22:58:18 fvdl Exp $	*/
 
 /*-
@@ -227,6 +227,7 @@ paddr_t avail_end;
 
 void (*delay_func)(int) = i8254_delay;
 void (*initclock_func)(void) = i8254_initclocks;
+void (*startclock_func)(void) = i8254_start_both_clocks;
 
 /*
  * Format of boot information passed to us by 32-bit /boot
@@ -1881,6 +1882,12 @@ 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/amd64/include/cpu.h b/sys/arch/amd64/include/cpu.h
index cf322886269..9069c3df8a8 100644
--- a/sys/arch/amd64/include/cpu.h
+++ b/sys/arch/amd64/include/cpu.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cpu.h,v 1.158 2023/07/27 00:28:24 guenther Exp $	*/
+/*	$OpenBSD: cpu.h,v 1.159 2023/08/23 01:55:46 cheloha Exp $	*/
 /*	$NetBSD: cpu.h,v 1.1 2003/04/26 18:39:39 fvdl Exp $	*/
 
 /*-
@@ -408,6 +408,8 @@ int	amd64_pa_used(paddr_t);
 extern void (*cpu_idle_cycle_fcn)(void);
 #define	cpu_idle_cycle()	(*cpu_idle_cycle_fcn)()
 #define	cpu_idle_leave()	do { /* nothing */ } while (0)
+extern void (*initclock_func)(void);
+extern void (*startclock_func)(void);
 
 struct region_descriptor;
 void	lgdt(struct region_descriptor *);
@@ -418,7 +420,6 @@ void	switch_exit(struct proc *, void (*)(struct proc *));
 void	proc_trampoline(void);
 
 /* clock.c */
-extern void (*initclock_func)(void);
 void	startclocks(void);
 void	rtcinit(void);
 void	rtcstart(void);
@@ -426,6 +427,7 @@ 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/amd64/isa/clock.c b/sys/arch/amd64/isa/clock.c
index 019259ffdff..3dd79b1769d 100644
--- a/sys/arch/amd64/isa/clock.c
+++ b/sys/arch/amd64/isa/clock.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: clock.c,v 1.40 2023/07/25 18:16:19 cheloha Exp $	*/
+/*	$OpenBSD: clock.c,v 1.41 2023/08/23 01:55:46 cheloha Exp $	*/
 /*	$NetBSD: clock.c,v 1.1 2003/04/26 18:39:50 fvdl Exp $	*/
 
 /*-
@@ -284,7 +284,11 @@ 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);
 
 	/*