cpu/hotplug: Document states better

Requested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 46 insertions, 1 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index bcee286b7c73..6ea42e8da861 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1172,6 +1172,10 @@ static struct cpuhp_step cpuhp_bp_states[] = {
                 .teardown               = NULL,
                 .cant_stop              = true,
         },
+        /*
+         * Preparatory and dead notifiers. Will be replaced once the notifiers
+         * are converted to states.
+         */
         [CPUHP_NOTIFY_PREPARE] = {
                 .name                   = "notify:prepare",
                 .startup                = notify_prepare,
@@ -1179,12 +1183,17 @@ static struct cpuhp_step cpuhp_bp_states[] = {
                 .skip_onerr             = true,
                 .cant_stop              = true,
         },
+        /* Kicks the plugged cpu into life */
         [CPUHP_BRINGUP_CPU] = {
                 .name                   = "cpu:bringup",
                 .startup                = bringup_cpu,
                 .teardown               = NULL,
                 .cant_stop              = true,
         },
+        /*
+         * Handled on controll processor until the plugged processor manages
+         * this itself.
+         */
         [CPUHP_TEARDOWN_CPU] = {
                 .name                   = "cpu:teardown",
                 .startup                = NULL,
@@ -1197,6 +1206,23 @@ static struct cpuhp_step cpuhp_bp_states[] = {
 /* Application processor state steps */
 static struct cpuhp_step cpuhp_ap_states[] = {
 #ifdef CONFIG_SMP
+        /* Final state before CPU kills itself */
+        [CPUHP_AP_IDLE_DEAD] = {
+                .name                   = "idle:dead",
+        },
+        /*
+         * Last state before CPU enters the idle loop to die. Transient state
+         * for synchronization.
+         */
+        [CPUHP_AP_OFFLINE] = {
+                .name                   = "ap:offline",
+                .cant_stop              = true,
+        },
+        /*
+         * Low level startup/teardown notifiers. Run with interrupts
+         * disabled. Will be removed once the notifiers are converted to
+         * states.
+         */
         [CPUHP_AP_NOTIFY_STARTING] = {
                 .name                   = "notify:starting",
                 .startup                = notify_starting,
@@ -1204,17 +1230,32 @@ static struct cpuhp_step cpuhp_ap_states[] = {
                 .skip_onerr             = true,
                 .cant_stop              = true,
         },
+        /* Entry state on starting. Interrupts enabled from here on. Transient
+         * state for synchronsization */
+        [CPUHP_AP_ONLINE] = {
+                .name                   = "ap:online",
+        },
+        /* Handle smpboot threads park/unpark */
         [CPUHP_AP_SMPBOOT_THREADS] = {
                 .name                   = "smpboot:threads",
                 .startup                = smpboot_unpark_threads,
                 .teardown               = NULL,
         },
+        /*
+         * Online/down_prepare notifiers. Will be removed once the notifiers
+         * are converted to states.
+         */
         [CPUHP_AP_NOTIFY_ONLINE] = {
                 .name                   = "notify:online",
                 .startup                = notify_online,
                 .teardown               = notify_down_prepare,
         },
 #endif
+        /*
+         * The dynamically registered state space is here
+         */
+
+        /* CPU is fully up and running. */
         [CPUHP_ONLINE] = {
                 .name                   = "online",
                 .startup                = NULL,
@@ -1232,7 +1273,11 @@ static int cpuhp_cb_check(enum cpuhp_state state)
 
 static bool cpuhp_is_ap_state(enum cpuhp_state state)
 {
-        return state > CPUHP_BRINGUP_CPU;
+        /*
+         * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
+         * purposes as that state is handled explicitely in cpu_down.
+         */
+        return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
 }
 
 static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)