[PATCH 03/13] openrisc: add 1 and 2 byte cmpxchg support

Stafford Horne
2017-08-30T22:00:24Z

OpenRISC only supports hardware instructions that perform 4 byte atomic
operations. For enabling qrwlocks for upcoming SMP support 1 and 2 byte
implementations are needed. To do this we leverage the 4 byte atomic
operations and shift/mask the 1 and 2 byte areas as needed.

This heavily borrows ideas and routines from sh and mips, which do
something similar.

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Stafford Horne <shorne@gmail.com>
---
arch/openrisc/include/asm/cmpxchg.h | 147 ++++++++++++++++++++++++++++--------
1 file changed, 115 insertions(+), 32 deletions(-)

diff --git a/arch/openrisc/include/asm/cmpxchg.h b/arch/openrisc/include/asm/cmpxchg.h
index f0a5d8b844d6..d29f7db53906 100644
--- a/arch/openrisc/include/asm/cmpxchg.h
+++ b/arch/openrisc/include/asm/cmpxchg.h
@@ -1,32 +1,29 @@
/*
+ * 1,2 and 4 byte cmpxchg and xchg implementations for OpenRISC.
+ *
* Copyright (C) 2014 Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
+ * Copyright (C) 2017 Stafford Horne <shorne@gmail.com>
*
* This file is licensed under the terms of the GNU General Public License
* version 2. This program is licensed "as is" without any warranty of any
* kind, whether express or implied.
+ *
+ * Note:
+ * The portable implementations of 1 and 2 byte xchg and cmpxchg using a 4
+ * byte cmpxchg is sourced heavily from the sh and mips implementations.
*/

#ifndef __ASM_OPENRISC_CMPXCHG_H
#define __ASM_OPENRISC_CMPXCHG_H

#include <linux/types.h>
-
-/*
- * This function doesn't exist, so you'll get a linker error
- * if something tries to do an invalid cmpxchg().
- */
-extern void __cmpxchg_called_with_bad_pointer(void);
+#include <linux/bitops.h>

#define __HAVE_ARCH_CMPXCHG 1

-static inline unsigned long
-__cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
+static inline unsigned long cmpxchg_u32(volatile void *ptr,
+ unsigned long old, unsigned long new)
{
- if (size != 4) {
- __cmpxchg_called_with_bad_pointer();
- return old;
- }
-
__asm__ __volatile__(
"1: l.lwa %0, 0(%1) \n"
" l.sfeq %0, %2 \n"
@@ -43,6 +40,97 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
return old;
}

+static inline unsigned long xchg_u32(volatile void *ptr,
+ unsigned long val)
+{
+ __asm__ __volatile__(
+ "1: l.lwa %0, 0(%1) \n"
+ " l.swa 0(%1), %2 \n"
+ " l.bnf 1b \n"
+ " l.nop \n"
+ : "=&r"(val)
+ : "r"(ptr), "r"(val)
+ : "cc", "memory");
+
+ return val;
+}
+
+static inline u32 cmpxchg_small(volatile void *ptr, u32 old, u32 new,
+ int size)
+{
+ int off = (unsigned long)ptr % sizeof(u32);
+ volatile u32 *p = ptr - off;
+#ifdef __BIG_ENDIAN
+ int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
+#else
+ int bitoff = off * BITS_PER_BYTE;
+#endif
+ u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
+ u32 load32, old32, new32;
+ u32 ret;
+
+ load32 = READ_ONCE(*p);
+
+ while (true) {
+ ret = (load32 & bitmask) >> bitoff;
+ if (old != ret)
+ return ret;
+
+ old32 = (load32 & ~bitmask) | (old << bitoff);
+ new32 = (load32 & ~bitmask) | (new << bitoff);
+
+ /* Do 32 bit cmpxchg */
+ load32 = cmpxchg_u32(p, old32, new32);
+ if (load32 == old32)
+ return old;
+ }
+}
+
+/* xchg */
+
+static inline u32 xchg_small(volatile void *ptr, u32 x, int size)
+{
+ int off = (unsigned long)ptr % sizeof(u32);
+ volatile u32 *p = ptr - off;
+#ifdef __BIG_ENDIAN
+ int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
+#else
+ int bitoff = off * BITS_PER_BYTE;
+#endif
+ u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
+ u32 oldv, newv;
+ u32 ret;
+
+ do {
+ oldv = READ_ONCE(*p);
+ ret = (oldv & bitmask) >> bitoff;
+ newv = (oldv & ~bitmask) | (x << bitoff);
+ } while (cmpxchg_u32(p, oldv, newv) != oldv);
+
+ return ret;
+}
+
+/*
+ * This function doesn't exist, so you'll get a linker error
+ * if something tries to do an invalid cmpxchg().
+ */
+extern unsigned long __cmpxchg_called_with_bad_pointer(void)
+ __compiletime_error("Bad argument size for cmpxchg");
+
+static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
+ unsigned long new, int size)
+{
+ switch (size) {
+ case 1:
+ case 2:
+ return cmpxchg_small(ptr, old, new, size);
+ case 4:
+ return cmpxchg_u32(ptr, old, new);
+ default:
+ return __cmpxchg_called_with_bad_pointer();
+ }
+}
+
#define cmpxchg(ptr, o, n) \
({ \
(__typeof__(*(ptr))) __cmpxchg((ptr), \
@@ -55,32 +143,27 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
* This function doesn't exist, so you'll get a linker error if
* something tries to do an invalidly-sized xchg().
*/
-extern void __xchg_called_with_bad_pointer(void);
+extern unsigned long __xchg_called_with_bad_pointer(void)
+ __compiletime_error("Bad argument size for xchg");

-static inline unsigned long __xchg(unsigned long val, volatile void *ptr,
- int size)
+static inline unsigned long __xchg(volatile void *ptr, unsigned long with,
+ int size)
{
- if (size != 4) {
- __xchg_called_with_bad_pointer();
- return val;
+ switch (size) {
+ case 1:
+ case 2:
+ return xchg_small(ptr, with, size);
+ case 4:
+ return xchg_u32(ptr, with);
+ default:
+ return __xchg_called_with_bad_pointer();
}
-
- __asm__ __volatile__(
- "1: l.lwa %0, 0(%1) \n"
- " l.swa 0(%1), %2 \n"
- " l.bnf 1b \n"
- " l.nop \n"
- : "=&r"(val)
- : "r"(ptr), "r"(val)
- : "cc", "memory");
-
- return val;
}

#define xchg(ptr, with) \
({ \
- (__typeof__(*(ptr))) __xchg((unsigned long)(with), \
- (ptr), \
+ (__typeof__(*(ptr))) __xchg((ptr), \
+ (unsigned long)(with), \
sizeof(*(ptr))); \
})

--
2.13.5