[RFC PATCH v2 07/15] xen/arm: prepare existing Xen headers for Linux atomics

[Ash Wilding <ash.j.wilding@xxxxxxxxx>]

From: Ash Wilding <ash.j.wilding@xxxxxxxxx>

This small patch helps prepare <asm-arm/atomic.h> and the arm32/arm64
specific system.h headers to play nicely with the Linux atomics helpers:

 - We don't need the indirection around atomic_add_unless() anymore so
   let's just pull up the old Xen arm64 definition into here and use it
   for both arm32 and arm64.

 - We don't need an atomic_xchg() in <asm-arm/atomic.h> as the arm32/arm64
   specific cmpxchg.h from Linux defines it for us.

 - We drop the includes of <asm/system.h> and <xen/prefetch.h> from
   <asm-arm/atomic.h> as they're not needed.

 - We swap out the include of the arm32/arm64 specific cmpxchg.h in the
   arm32/arm64 specific system.h and instead make them include atomic.h;
   this works around build issues from cmpxchg.h trying to use the
   __ll_sc_lse_body() macro before it's ready.

Signed-off-by: Ash Wilding <ash.j.wilding@xxxxxxxxx>
---
 xen/include/asm-arm/arm32/system.h |  2 +-
 xen/include/asm-arm/arm64/system.h |  2 +-
 xen/include/asm-arm/atomic.h       | 15 +++++++++++----
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/xen/include/asm-arm/arm32/system.h 
b/xen/include/asm-arm/arm32/system.h
index ab57abfbc5..88798d11db 100644
--- a/xen/include/asm-arm/arm32/system.h
+++ b/xen/include/asm-arm/arm32/system.h
@@ -2,7 +2,7 @@
 #ifndef __ASM_ARM32_SYSTEM_H
 #define __ASM_ARM32_SYSTEM_H
 
-#include <asm/arm32/cmpxchg.h>
+#include <asm/atomic.h>
 
 #define local_irq_disable() asm volatile ( "cpsid i @ local_irq_disable\n" : : 
: "cc" )
 #define local_irq_enable()  asm volatile ( "cpsie i @ local_irq_enable\n" : : 
: "cc" )
diff --git a/xen/include/asm-arm/arm64/system.h 
b/xen/include/asm-arm/arm64/system.h
index 2e36573ac6..dfbbe4b87d 100644
--- a/xen/include/asm-arm/arm64/system.h
+++ b/xen/include/asm-arm/arm64/system.h
@@ -2,7 +2,7 @@
 #ifndef __ASM_ARM64_SYSTEM_H
 #define __ASM_ARM64_SYSTEM_H
 
-#include <asm/arm64/cmpxchg.h>
+#include <asm/atomic.h>
 
 /* Uses uimm4 as a bitmask to select the clearing of one or more of
  * the DAIF exception mask bits:
diff --git a/xen/include/asm-arm/atomic.h b/xen/include/asm-arm/atomic.h
index ac2798d095..866f54d03c 100644
--- a/xen/include/asm-arm/atomic.h
+++ b/xen/include/asm-arm/atomic.h
@@ -2,8 +2,6 @@
 #define __ARCH_ARM_ATOMIC__
 
 #include <xen/atomic.h>
-#include <xen/prefetch.h>
-#include <asm/system.h>
 
 #define build_atomic_read(name, size, width, type) \
 static inline type name(const volatile type *addr) \
@@ -220,10 +218,19 @@ static inline int atomic_add_negative(int i, atomic_t *v)
 
 static inline int atomic_add_unless(atomic_t *v, int a, int u)
 {
-    return __atomic_add_unless(v, a, u);
+       int c, old;
+
+       c = atomic_read(v);
+       while (c != u && (old = atomic_cmpxchg((v), c, c + a)) != c)
+               c = old;
+
+       return c;
 }
 
-#define atomic_xchg(v, new) (xchg(&((v)->counter), new))
+static inline int atomic_cmpxchg(atomic_t *v, int old, int new)
+{
+       return cmpxchg(&((v)->counter), (old), (new));
+}
 
 #endif /* __ARCH_ARM_ATOMIC__ */
 /*
-- 
2.24.3 (Apple Git-128)