powerpc: Allow the max stack trace depth to be configured

On my screen, when something crashes, I only have space for maybe 16
functions of the stack trace before the information above it scrolls
off the screen.  It's easy to hack the kernel to print out only that
much, but it's harder to remember to do it.  This introduces a config
option for it so that I can keep the setting in my config.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/Kconfig.debug

@@ -2,6 +2,15 @@ menu "Kernel hacking"
 
 source "lib/Kconfig.debug"
 
+config PRINT_STACK_DEPTH
+	int "Stack depth to print" if DEBUG_KERNEL
+	default 64
+	help
+	  This option allows you to set the stack depth that the kernel
+	  prints in stack traces. This can be useful if your display is
+	  too small and stack traces cause important information to
+	  scroll off the screen.
+
 config DEBUG_STACKOVERFLOW
 	bool "Check for stack overflows"
 	depends on DEBUG_KERNEL

arch/powerpc/kernel/process.c

@@ -1000,7 +1000,7 @@ unsigned long get_wchan(struct task_struct *p)
 	return 0;
 }
 
-static int kstack_depth_to_print = 64;
+static int kstack_depth_to_print = CONFIG_PRINT_STACK_DEPTH;
 
 void show_stack(struct task_struct *tsk, unsigned long *stack)
 {