git: 602c858e000d - main - arm64: Reuse aps_started to simplify SMP boot

The branch main has been updated by andrew:

URL: https://cgit.FreeBSD.org/src/commit/?id=602c858e000dafd81bbfbdaf72588fef18fea938

commit 602c858e000dafd81bbfbdaf72588fef18fea938
Author:     Andrew Turner <andrew@FreeBSD.org>
AuthorDate: 2025-05-27 19:38:29 +0000
Commit:     Andrew Turner <andrew@FreeBSD.org>
CommitDate: 2025-05-27 19:50:11 +0000

    arm64: Reuse aps_started to simplify SMP boot
    
    We need to know when all CPUs have booted. Rather than locking and
    counting when starting CPUs we can count on the boot CPU to set
    smp_started.
    
    Sponsored by:   Arm Ltd
    Differential Revision:  https://reviews.freebsd.org/D50366
---
 sys/arm64/arm64/mp_machdep.c | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/sys/arm64/arm64/mp_machdep.c b/sys/arm64/arm64/mp_machdep.c
index 4ef0019d3f8f..88d48bceb892 100644
--- a/sys/arm64/arm64/mp_machdep.c
+++ b/sys/arm64/arm64/mp_machdep.c
@@ -112,9 +112,6 @@ void mpentry_psci(unsigned long cpuid);
 void mpentry_spintable(void);
 void init_secondary(uint64_t);
 
-/* Synchronize AP startup. */
-static struct mtx ap_boot_mtx;
-
 /* Used to initialize the PCPU ahead of calling init_secondary(). */
 void *bootpcpu;
 uint64_t ap_cpuid;
@@ -143,16 +140,19 @@ static bool
 wait_for_aps(void)
 {
 	for (int i = 0, started = 0; i < 2000; i++) {
-		if (atomic_load_acq_int(&smp_started) != 0) {
+		int32_t nstarted;
+
+		nstarted = atomic_load_32(&aps_started);
+		if (nstarted == mp_ncpus - 1)
 			return (true);
-		}
+
 		/*
 		 * Don't time out while we are making progress. Some large
 		 * systems can take a while to start all CPUs.
 		 */
-		if (smp_cpus > started) {
+		if (nstarted > started) {
 			i = 0;
-			started = smp_cpus;
+			started = nstarted;
 		}
 		DELAY(1000);
 	}
@@ -174,6 +174,7 @@ release_aps(void *dummy __unused)
 	intr_ipi_setup(IPI_STOP_HARD, "stop hard", ipi_stop, NULL);
 	intr_ipi_setup(IPI_HARDCLOCK, "hardclock", ipi_hardclock, NULL);
 
+	atomic_store_int(&aps_started, 0);
 	atomic_store_rel_int(&aps_ready, 1);
 	/* Wake up the other CPUs */
 	__asm __volatile(
@@ -187,6 +188,9 @@ release_aps(void *dummy __unused)
 		printf("done\n");
 	else
 		printf("APs not started\n");
+
+	smp_cpus = atomic_load_int(&aps_started) + 1;
+	atomic_store_rel_int(&smp_started, 1);
 }
 SYSINIT(start_aps, SI_SUB_SMP, SI_ORDER_FIRST, release_aps, NULL);
 
@@ -263,13 +267,8 @@ init_secondary(uint64_t cpu)
 
 	dbg_init();
 
-	mtx_lock_spin(&ap_boot_mtx);
-	atomic_add_rel_32(&smp_cpus, 1);
-	if (smp_cpus == mp_ncpus) {
-		/* enable IPI's, tlb shootdown, freezes etc */
-		atomic_store_rel_int(&smp_started, 1);
-	}
-	mtx_unlock_spin(&ap_boot_mtx);
+	/* Signal the CPU is ready */
+	atomic_add_int(&aps_started, 1);
 
 	kcsan_cpu_init(cpu);
 
@@ -700,8 +699,6 @@ cpu_mp_start(void)
 {
 	uint64_t mpidr;
 
-	mtx_init(&ap_boot_mtx, "ap boot", NULL, MTX_SPIN);
-
 	/* CPU 0 is always boot CPU. */
 	CPU_SET(0, &all_cpus);
 	mpidr = READ_SPECIALREG(mpidr_el1) & CPU_AFF_MASK;