[ARM] Add thread_notify infrastructure

Some machine classes need to allow VFP support to be built into the
kernel, but still allow the kernel to run even though VFP isn't
present.  Unfortunately, the kernel hard-codes VFP instructions
into the thread switch, which prevents this being run-time selectable.

Solve this by introducing a notifier which things such as VFP can
hook into to be informed of events which affect the VFP subsystem
(eg, creation and destruction of threads, switches between threads.)

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 19 insertions, 6 deletions

diff --git a/arch/arm/nwfpe/fpmodule.c b/arch/arm/nwfpe/fpmodule.c
index 2dfe1ac42ee8..7d977d23f026 100644
--- a/arch/arm/nwfpe/fpmodule.c
+++ b/arch/arm/nwfpe/fpmodule.c
@@ -33,7 +33,8 @@
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/init.h>
-/* XXX */
+
+#include <asm/thread_notify.h>
 
 #include "softfloat.h"
 #include "fpopcode.h"
@@ -56,16 +57,28 @@ void fp_send_sig(unsigned long sig, struct task_struct *p, int priv);
 extern char fpe_type[];
 #endif
 
+static int nwfpe_notify(struct notifier_block *self, unsigned long cmd, void *v)
+{
+        struct thread_info *thread = v;
+
+        if (cmd == THREAD_NOTIFY_FLUSH)
+                nwfpe_init_fpa(&thread->fpstate);
+
+        return NOTIFY_DONE;
+}
+
+static struct notifier_block nwfpe_notifier_block = {
+        .notifier_call = nwfpe_notify,
+};
+
 /* kernel function prototypes required */
 void fp_setup(void);
 
 /* external declarations for saved kernel symbols */
 extern void (*kern_fp_enter)(void);
-extern void (*fp_init)(union fp_state *);
 
 /* Original value of fp_enter from kernel before patched by fpe_init. */
 static void (*orig_fp_enter)(void);
-static void (*orig_fp_init)(union fp_state *);
 
 /* forward declarations */
 extern void nwfpe_enter(void);
@@ -88,20 +101,20 @@ static int __init fpe_init(void)
         printk(KERN_WARNING "NetWinder Floating Point Emulator V0.97 ("
                NWFPE_BITS " precision)\n");
 
+        thread_register_notifier(&nwfpe_notifier_block);
+
         /* Save pointer to the old FP handler and then patch ourselves in */
         orig_fp_enter = kern_fp_enter;
-        orig_fp_init = fp_init;
         kern_fp_enter = nwfpe_enter;
-        fp_init = nwfpe_init_fpa;
 
         return 0;
 }
 
 static void __exit fpe_exit(void)
 {
+        thread_unregister_notifier(&nwfpe_notifier_block);
         /* Restore the values we saved earlier. */
         kern_fp_enter = orig_fp_enter;
-        fp_init = orig_fp_init;
 }
 
 /*