[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>

3 files changed, 22 insertions, 28 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index ab8e600c18c8..86c92523a346 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -20,6 +20,7 @@
 #include <asm/glue.h>
 #include <asm/vfpmacros.h>
 #include <asm/arch/entry-macro.S>
+#include <asm/thread_notify.h>
 
 #include "entry-header.S"
 
@@ -560,10 +561,8 @@ ENTRY(__switch_to)
 	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
@@ -585,21 +584,20 @@ ENTRY(__switch_to)
 #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
 
diff --git a/arch/arm/kernel/iwmmxt.S b/arch/arm/kernel/iwmmxt.S
index 24c7b0477a09..af9e0ae952d5 100644
--- a/arch/arm/kernel/iwmmxt.S
+++ b/arch/arm/kernel/iwmmxt.S
@@ -285,7 +285,7 @@ ENTRY(iwmmxt_task_switch)
 	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
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 17c38dbf2f3c..e1c77ee885a7 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -33,6 +33,7 @@
 #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>
 
@@ -338,13 +339,9 @@ void exit_thread(void)
 {
 }
 
-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)
 {
@@ -353,22 +350,21 @@ 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
 }