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

1 files changed, 5 insertions, 1 deletions

diff --git a/sys/arch/alpha/alpha/clock.c b/sys/arch/alpha/alpha/clock.c
index c03cd35993d..dd3ad3f75b2 100644
--- a/sys/arch/alpha/alpha/clock.c
+++ b/sys/arch/alpha/alpha/clock.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: clock.c,v 1.29 2023/08/21 15:19:09 cheloha Exp $	*/
+/*	$OpenBSD: clock.c,v 1.30 2023/08/23 01:55:45 cheloha Exp $	*/
 /*	$NetBSD: clock.c,v 1.29 2000/06/05 21:47:10 thorpej Exp $	*/
 
 /*
@@ -192,7 +192,11 @@ cpu_initclocks(void)
 	stathz = hz;
 	profhz = stathz;
 	clockintr_init(0);
+}
 
+void
+cpu_startclock(void)
+{
 	clockintr_cpu_init(NULL);
 
 	/*