[PATCH] ARM: 2664/2: add support for atomic ops on pre-ARMv6 SMP systems
Patch from Nicolas Pitre
Not that there might be many of them on the planet, but at least RMK
apparently has one.
Signed-off-by: Nicolas Pitre
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 4eb3615..e14278d 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -269,7 +269,7 @@
add r5, sp, #S_PC
ldmia r7, {r2 - r4} @ Get USR pc, cpsr
-#if __LINUX_ARM_ARCH__ < 6
+#if __LINUX_ARM_ARCH__ < 6 && !defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
@ make sure our user space atomic helper is aborted
cmp r2, #VIRT_OFFSET
bichs r3, r3, #PSR_Z_BIT
@@ -616,11 +616,17 @@
__kuser_cmpxchg: @ 0xffff0fc0
-#if __LINUX_ARM_ARCH__ < 6
+#if defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
-#ifdef CONFIG_SMP /* sanity check */
-#error "CONFIG_SMP on a machine supporting pre-ARMv6 processors?"
-#endif
+ /*
+ * Poor you. No fast solution possible...
+ * The kernel itself must perform the operation.
+ * A special ghost syscall is used for that (see traps.c).
+ */
+ swi #0x9ffff0
+ mov pc, lr
+
+#elif __LINUX_ARM_ARCH__ < 6
/*
* Theory of operation: