powerpc/kexec: Add to and tidy debug/comments in machine_kexec64.c

Tidies some typos, KERN_INFO-ise an info msg, and add a debug msg showing
when the final sequence starts.

Also adds a comment to kexec_prepare_cpus_wait() to make note of a possible
problem; the need for kexec to deal with CPUs that failed to originally start
up.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 24 insertions, 5 deletions

diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index 022d2f613b7b..a0bcec3614e1 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -15,6 +15,7 @@
 #include <linux/thread_info.h>
 #include <linux/init_task.h>
 #include <linux/errno.h>
+#include <linux/kernel.h>
 
 #include <asm/page.h>
 #include <asm/current.h>
@@ -184,7 +185,20 @@ static void kexec_prepare_cpus_wait(int wait_state)
 
         hw_breakpoint_disable();
         my_cpu = get_cpu();
-        /* Make sure each CPU has atleast made it to the state we need */
+        /* Make sure each CPU has at least made it to the state we need.
+         *
+         * FIXME: There is a (slim) chance of a problem if not all of the CPUs
+         * are correctly onlined.  If somehow we start a CPU on boot with RTAS
+         * start-cpu, but somehow that CPU doesn't write callin_cpu_map[] in
+         * time, the boot CPU will timeout.  If it does eventually execute
+         * stuff, the secondary will start up (paca[].cpu_start was written) and
+         * get into a peculiar state.  If the platform supports
+         * smp_ops->take_timebase(), the secondary CPU will probably be spinning
+         * in there.  If not (i.e. pseries), the secondary will continue on and
+         * try to online itself/idle/etc. If it survives that, we need to find
+         * these possible-but-not-online-but-should-be CPUs and chaperone them
+         * into kexec_smp_wait().
+         */
         for_each_online_cpu(i) {
                 if (i == my_cpu)
                         continue;
@@ -192,9 +206,9 @@ static void kexec_prepare_cpus_wait(int wait_state)
                 while (paca[i].kexec_state < wait_state) {
                         barrier();
                         if (i != notified) {
-                                printk( "kexec: waiting for cpu %d (physical"
-                                                " %d) to enter %i state\n",
-                                        i, paca[i].hw_cpu_id, wait_state);
+                                printk(KERN_INFO "kexec: waiting for cpu %d "
+                                       "(physical %d) to enter %i state\n",
+                                       i, paca[i].hw_cpu_id, wait_state);
                                 notified = i;
                         }
                 }
@@ -218,7 +232,10 @@ static void kexec_prepare_cpus(void)
         if (ppc_md.kexec_cpu_down)
                 ppc_md.kexec_cpu_down(0, 0);
 
-        /* Before removing MMU mapings make sure all CPUs have entered real mode */
+        /*
+         * Before removing MMU mappings make sure all CPUs have entered real
+         * mode:
+         */
         kexec_prepare_cpus_wait(KEXEC_STATE_REAL_MODE);
 
         put_cpu();
@@ -287,6 +304,8 @@ void default_machine_kexec(struct kimage *image)
         if (crashing_cpu == -1)
                 kexec_prepare_cpus();
 
+        pr_debug("kexec: Starting switchover sequence.\n");
+
         /* switch to a staticly allocated stack.  Based on irq stack code.
          * XXX: the task struct will likely be invalid once we do the copy!
          */