[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, 48 insertions, 0 deletions

diff --git a/include/asm-arm/thread_notify.h b/include/asm-arm/thread_notify.h
new file mode 100644
index 00000000000..8866e521684
--- /dev/null
+++ b/include/asm-arm/thread_notify.h
@@ -0,0 +1,48 @@
+/*
+ *  linux/include/asm-arm/thread_notify.h
+ *
+ *  Copyright (C) 2006 Russell King.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#ifndef ASMARM_THREAD_NOTIFY_H
+#define ASMARM_THREAD_NOTIFY_H
+
+#ifdef __KERNEL__
+
+#ifndef __ASSEMBLY__
+
+#include <linux/notifier.h>
+#include <asm/thread_info.h>
+
+static inline int thread_register_notifier(struct notifier_block *n)
+{
+	extern struct atomic_notifier_head thread_notify_head;
+	return atomic_notifier_chain_register(&thread_notify_head, n);
+}
+
+static inline void thread_unregister_notifier(struct notifier_block *n)
+{
+	extern struct atomic_notifier_head thread_notify_head;
+	atomic_notifier_chain_unregister(&thread_notify_head, n);
+}
+
+static inline void thread_notify(unsigned long rc, struct thread_info *thread)
+{
+	extern struct atomic_notifier_head thread_notify_head;
+	atomic_notifier_call_chain(&thread_notify_head, rc, thread);
+}
+
+#endif
+
+/*
+ * These are the reason codes for the thread notifier.
+ */
+#define THREAD_NOTIFY_FLUSH	0
+#define THREAD_NOTIFY_RELEASE	1
+#define THREAD_NOTIFY_SWITCH	2
+
+#endif
+#endif