macppc, powerpc64: dec_rearm: no need to disable interrupts

[Scott Cheloha]

On macppc and powerpc64, I don't think we need to disable interrupts
during dec_rearm().  ppc_mtdec() and mtdec() are just:

        mtspr   dec,<register>

or

        mtdec   <register>

which is atomic.

Tested on macpcc (my G4).  Kernel boots, system has been up for over
24 hours doing a parallel `make build`.

When I wrote dec_rearm() I think I was just imitating dec_trigger().
In that case, we *do* need to disable interrupts because we're doing
mtspr twice.

ok?

Index: macppc/macppc/clock.c
===================================================================
RCS file: /cvs/src/sys/arch/macppc/macppc/clock.c,v
retrieving revision 1.52
diff -u -p -r1.52 clock.c
--- macppc/macppc/clock.c       27 Jan 2023 22:13:48 -0000      1.52
+++ macppc/macppc/clock.c       28 Jan 2023 23:20:06 -0000
@@ -248,16 +248,13 @@ void
 dec_rearm(void *unused, uint64_t nsecs)
 {
        uint32_t cycles;
-       int s;
 
        if (nsecs > dec_nsec_max)
                nsecs = dec_nsec_max;
        cycles = (nsecs * dec_nsec_cycle_ratio) >> 32;
        if (cycles > UINT32_MAX >> 1)
                cycles = UINT32_MAX >> 1;
-       s = ppc_intr_disable();
        ppc_mtdec(cycles);
-       ppc_intr_enable(s);
 }
 
 void
Index: powerpc64/powerpc64/clock.c
===================================================================
RCS file: /cvs/src/sys/arch/powerpc64/powerpc64/clock.c,v
retrieving revision 1.8
diff -u -p -r1.8 clock.c
--- powerpc64/powerpc64/clock.c 27 Jan 2023 22:14:43 -0000      1.8
+++ powerpc64/powerpc64/clock.c 28 Jan 2023 23:20:06 -0000
@@ -59,7 +59,6 @@ void  cpu_startclock(void);
 void
 dec_rearm(void *unused, uint64_t nsecs)
 {
-       u_long s;
        uint32_t cycles;
 
        if (nsecs > dec_nsec_max)
@@ -67,9 +66,7 @@ dec_rearm(void *unused, uint64_t nsecs)
        cycles = (nsecs * dec_nsec_cycle_ratio) >> 32;
        if (cycles > UINT32_MAX >> 1)
                cycles = UINT32_MAX >> 1;
-       s = intr_disable();
        mtdec(cycles);
-       intr_restore(s);
 }
 
 void