[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 <[e-mail]>

arch/arm/kernel/entry-armv.S

···
 #include <asm/glue.h>
 #include <asm/vfpmacros.h>
 #include <asm/arch/entry-macro.S>
+#include <asm/thread_notify.h>
 
 #include "entry-header.S"
 
···
 	add	ip, r1, #TI_CPU_SAVE
 	ldr	r3, [r2, #TI_TP_VALUE]
 	stmia	ip!, {r4 - sl, fp, sp, lr}	@ Store most regs on stack
-#ifndef CONFIG_MMU
-	add	r2, r2, #TI_CPU_DOMAIN
-#else
-	ldr	r6, [r2, #TI_CPU_DOMAIN]!
+#ifdef CONFIG_MMU
+	ldr	r6, [r2, #TI_CPU_DOMAIN]
 #endif
 #if __LINUX_ARM_ARCH__ >= 6
 #ifdef CONFIG_CPU_32v6K
···
 #ifdef CONFIG_MMU
 	mcr	p15, 0, r6, c3, c0, 0		@ Set domain register
 #endif
-#ifdef CONFIG_VFP
-	@ Always disable VFP so we can lazily save/restore the old
-	@ state. This occurs in the context of the previous thread.
-	VFPFMRX	r4, FPEXC
-	bic	r4, r4, #FPEXC_ENABLE
-	VFPFMXR	FPEXC, r4
-#endif
 #if defined(CONFIG_IWMMXT)
 	bl	iwmmxt_task_switch
 #elif defined(CONFIG_CPU_XSCALE)
-	add	r4, r2, #40			@ cpu_context_save->extra
+	add	r4, r2, #TI_CPU_DOMAIN + 40	@ cpu_context_save->extra
 	ldmib	r4, {r4, r5}
 	mar	acc0, r4, r5
 #endif
-	ldmib	r2, {r4 - sl, fp, sp, pc}	@ Load all regs saved previously
+	mov	r5, r0
+	add	r4, r2, #TI_CPU_SAVE
+	ldr	r0, =thread_notify_head
+	mov	r1, #THREAD_NOTIFY_SWITCH
+	bl	atomic_notifier_call_chain
+	mov	r0, r5
+	ldmia	r4, {r4 - sl, fp, sp, pc}	@ Load all regs saved previously
 
 	__INIT
 

arch/arm/kernel/iwmmxt.S

···
 	bne	1f				@ yes: block them for next task
 
 	ldr	r5, =concan_owner
-	add	r6, r2, #(TI_IWMMXT_STATE - TI_CPU_DOMAIN) @ get next task Concan save area
+	add	r6, r2, #TI_IWMMXT_STATE	@ get next task Concan save area
 	ldr	r5, [r5]			@ get current Concan owner
 	teq	r5, r6				@ next task owns it?
 	movne	pc, lr				@ no: leave Concan disabled

arch/arm/kernel/process.c

···
 #include <asm/leds.h>
 #include <asm/processor.h>
 #include <asm/system.h>
+#include <asm/thread_notify.h>
 #include <asm/uaccess.h>
 #include <asm/mach/time.h>
 
···
 {
 }
 
-static void default_fp_init(union fp_state *fp)
-{
-	memset(fp, 0, sizeof(union fp_state));
-}
+ATOMIC_NOTIFIER_HEAD(thread_notify_head);
 
-void (*fp_init)(union fp_state *) = default_fp_init;
-EXPORT_SYMBOL(fp_init);
+EXPORT_SYMBOL_GPL(thread_notify_head);
 
 void flush_thread(void)
 {
···
 
 	memset(thread->used_cp, 0, sizeof(thread->used_cp));
 	memset(&tsk->thread.debug, 0, sizeof(struct debug_info));
+	memset(&thread->fpstate, 0, sizeof(union fp_state));
+
+	thread_notify(THREAD_NOTIFY_FLUSH, thread);
 #if defined(CONFIG_IWMMXT)
 	iwmmxt_task_release(thread);
-#endif
-	fp_init(&thread->fpstate);
-#if defined(CONFIG_VFP)
-	vfp_flush_thread(&thread->vfpstate);
 #endif
 }
 
 void release_thread(struct task_struct *dead_task)
 {
-#if defined(CONFIG_VFP)
-	vfp_release_thread(&task_thread_info(dead_task)->vfpstate);
-#endif
+	struct thread_info *thread = task_thread_info(dead_task);
+
+	thread_notify(THREAD_NOTIFY_RELEASE, thread);
 #if defined(CONFIG_IWMMXT)
-	iwmmxt_task_release(task_thread_info(dead_task));
+	iwmmxt_task_release(thread);
 #endif
 }
 

arch/arm/nwfpe/fpmodule.c

···
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/init.h>
-/* XXX */
+
+#include <asm/thread_notify.h>
 
 #include "softfloat.h"
 #include "fpopcode.h"
···
 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);
···
 	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;
 }
 
 /*

arch/arm/vfp/vfpmodule.c

···
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/init.h>
+
+#include <asm/thread_notify.h>
 #include <asm/vfp.h>
 
 #include "vfpinstr.h"
···
  */
 unsigned int VFP_arch;
 
-/*
- * Per-thread VFP initialisation.
- */
-void vfp_flush_thread(union vfp_state *vfp)
+static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
 {
-	memset(vfp, 0, sizeof(union vfp_state));
+	struct thread_info *thread = v;
+	union vfp_state *vfp = &thread->vfpstate;
 
-	vfp->hard.fpexc = FPEXC_ENABLE;
-	vfp->hard.fpscr = FPSCR_ROUND_NEAREST;
+	switch (cmd) {
+	case THREAD_NOTIFY_FLUSH:
+		/*
+		 * Per-thread VFP initialisation.
+		 */
+		memset(vfp, 0, sizeof(union vfp_state));
 
-	/*
-	 * Disable VFP to ensure we initialise it first.
-	 */
-	fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_ENABLE);
+		vfp->hard.fpexc = FPEXC_ENABLE;
+		vfp->hard.fpscr = FPSCR_ROUND_NEAREST;
 
-	/*
-	 * Ensure we don't try to overwrite our newly initialised
-	 * state information on the first fault.
-	 */
-	if (last_VFP_context == vfp)
-		last_VFP_context = NULL;
+		/*
+		 * Disable VFP to ensure we initialise it first.
+		 */
+		fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_ENABLE);
+
+		/*
+		 * FALLTHROUGH: Ensure we don't try to overwrite our newly
+		 * initialised state information on the first fault.
+		 */
+
+	case THREAD_NOTIFY_RELEASE:
+		/*
+		 * Per-thread VFP cleanup.
+		 */
+		if (last_VFP_context == vfp)
+			last_VFP_context = NULL;
+		break;
+
+	case THREAD_NOTIFY_SWITCH:
+		/*
+		 * Always disable VFP so we can lazily save/restore the
+		 * old state.
+		 */
+		fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_ENABLE);
+		break;
+	}
+
+	return NOTIFY_DONE;
 }
 
-/*
- * Per-thread VFP cleanup.
- */
-void vfp_release_thread(union vfp_state *vfp)
-{
-	if (last_VFP_context == vfp)
-		last_VFP_context = NULL;
-}
+static struct notifier_block vfp_notifier_block = {
+	.notifier_call	= vfp_notifier,
+};
 
 /*
  * Raise a SIGFPE for the current process.
···
 			(vfpsid & FPSID_VARIANT_MASK) >> FPSID_VARIANT_BIT,
 			(vfpsid & FPSID_REV_MASK) >> FPSID_REV_BIT);
 		vfp_vector = vfp_support_entry;
+
+		thread_register_notifier(&vfp_notifier_block);
 	}
 	return 0;
 }

include/asm-arm/thread_notify.h

···
+/*
+ *  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