[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, 11 insertions, 13 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