[POWERPC] Document when printk is useable

When debugging early boot problems, it's common to sprinkle printk's
all over the place.  However, on 64-bit powerpc, this can lead to
memory corruption if done too early due to the PACA pointer and
lockdep core not being initialized.

This adds some comments to early_setup() that document when it is
safe to do so in order to save time for whoever has to debug that
stuff next.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 25e3fd8606ab..f2cd82eaf49d 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -170,6 +170,8 @@ void __init setup_paca(int cpu)
 
 void __init early_setup(unsigned long dt_ptr)
 {
+        /* -------- printk is _NOT_ safe to use here ! ------- */
+
         /* Fill in any unititialised pacas */
         initialise_pacas();
 
@@ -185,6 +187,8 @@ void __init early_setup(unsigned long dt_ptr)
         /* Initialize lockdep early or else spinlocks will blow */
         lockdep_init();
 
+        /* -------- printk is now safe to use ------- */
+
         DBG(" -> early_setup(), dt_ptr: 0x%lx\n", dt_ptr);
 
         /*