microblaze: Lockdep support

Microblaze needs to do lock_init very soon because MMU init calls lock functions.

Here is the explanation from Peter Zijlstra why we have to enable
__ARCH_WANTS_INTERRUPTS_ON_CTSW.

"So we schedule while holding rq->lock (for obvious reasons), but since
lockdep tracks held locks per tasks, we need to transfer the held state
from the prev to the next task. We do this by explicity calling
spin_release(&rq->lock) in context_switch() right before switch_to(),
and calling spin_acquire(&rq->lock) in
finish_task_switch()->finish_lock_switch().

Now, for some reason lockdep thinks that interrupts got enabled over the
context switch (git grep __ARCH_WANTS_INTERRUPTS_ON_CTSW arch/microblaze
doesn't seem to turn up anything).

Clearly trying to acquire the rq->lock with interrupts enabled is a bad
idea and lockdep warns you about this."

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/Kconfig

@@ -60,6 +60,9 @@ config GENERIC_CSUM
 config STACKTRACE_SUPPORT
 	def_bool y
 
+config LOCKDEP_SUPPORT
+	def_bool y
+
 config PCI
 	def_bool n
 

arch/microblaze/include/asm/system.h

@@ -16,6 +16,8 @@
 #include <asm-generic/cmpxchg.h>
 #include <asm-generic/cmpxchg-local.h>
 
+#define __ARCH_WANT_INTERRUPTS_ON_CTXSW
+
 struct task_struct;
 struct thread_info;
 

arch/microblaze/kernel/setup.c

@@ -131,6 +131,8 @@ void __init machine_early_init(const char *cmdline, unsigned int ram,
 		strlcpy(cmd_line, cmdline, COMMAND_LINE_SIZE);
 #endif
 
+	lockdep_init();
+
 /* initialize device tree for usage in early_printk */
 	early_init_devtree((void *)_fdt_start);