arm64: klib: Optimised atomic bitops

This patch implements the AArch64-specific atomic bitops functions using
exclusive memory accesses to avoid locking.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

4 files changed, 94 insertions, 32 deletions

diff --git a/arch/arm64/include/asm/bitops.h b/arch/arm64/include/asm/bitops.h
index 5e693073b030..aa5b59d6ba43 100644
--- a/arch/arm64/include/asm/bitops.h
+++ b/arch/arm64/include/asm/bitops.h
@@ -32,6 +32,16 @@
 #error only <linux/bitops.h> can be included directly
 #endif
 
+/*
+ * Little endian assembly atomic bitops.
+ */
+extern void set_bit(int nr, volatile unsigned long *p);
+extern void clear_bit(int nr, volatile unsigned long *p);
+extern void change_bit(int nr, volatile unsigned long *p);
+extern int test_and_set_bit(int nr, volatile unsigned long *p);
+extern int test_and_clear_bit(int nr, volatile unsigned long *p);
+extern int test_and_change_bit(int nr, volatile unsigned long *p);
+
 #include <asm-generic/bitops/builtin-__ffs.h>
 #include <asm-generic/bitops/builtin-ffs.h>
 #include <asm-generic/bitops/builtin-__fls.h>
@@ -45,9 +55,13 @@
 #include <asm-generic/bitops/hweight.h>
 #include <asm-generic/bitops/lock.h>
 
-#include <asm-generic/bitops/atomic.h>
 #include <asm-generic/bitops/non-atomic.h>
 #include <asm-generic/bitops/le.h>
-#include <asm-generic/bitops/ext2-atomic.h>
+
+/*
+ * Ext2 is defined to use little-endian byte ordering.
+ */
+#define ext2_set_bit_atomic(lock, nr, p)        test_and_set_bit_le(nr, p)
+#define ext2_clear_bit_atomic(lock, nr, p)      test_and_clear_bit_le(nr, p)
 
 #endif /* __ASM_BITOPS_H */
diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c
index a5d0d4643109..7df1aad29b67 100644
--- a/arch/arm64/kernel/arm64ksyms.c
+++ b/arch/arm64/kernel/arm64ksyms.c
@@ -39,11 +39,6 @@ EXPORT_SYMBOL(__copy_from_user);
 EXPORT_SYMBOL(__copy_to_user);
 EXPORT_SYMBOL(__clear_user);
 
-        /* bitops */
-#ifdef CONFIG_SMP
-EXPORT_SYMBOL(__atomic_hash);
-#endif
-
         /* physical memory */
 EXPORT_SYMBOL(memstart_addr);
 
@@ -54,3 +49,11 @@ EXPORT_SYMBOL(memset);
 EXPORT_SYMBOL(memcpy);
 EXPORT_SYMBOL(memmove);
 EXPORT_SYMBOL(memchr);
+
+        /* atomic bitops */
+EXPORT_SYMBOL(set_bit);
+EXPORT_SYMBOL(test_and_set_bit);
+EXPORT_SYMBOL(clear_bit);
+EXPORT_SYMBOL(test_and_clear_bit);
+EXPORT_SYMBOL(change_bit);
+EXPORT_SYMBOL(test_and_change_bit);
diff --git a/arch/arm64/lib/bitops.S b/arch/arm64/lib/bitops.S
new file mode 100644
index 000000000000..fd1e801b53e7
--- /dev/null
+++ b/arch/arm64/lib/bitops.S
@@ -0,0 +1,70 @@
+/*
+ * Based on arch/arm/lib/bitops.h
+ *
+ * Copyright (C) 2013 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * x0: bits 5:0  bit offset
+ *     bits 63:6 word offset
+ * x1: address
+ */
+        .macro  bitop, name, instr
+ENTRY(  \name   )
+        and     x3, x0, #63             // Get bit offset
+        eor     x0, x0, x3              // Clear low bits
+        mov     x2, #1
+        add     x1, x1, x0, lsr #3      // Get word offset
+        lsl     x3, x2, x3              // Create mask
+1:      ldxr    x2, [x1]
+        \instr  x2, x2, x3
+        stxr    w0, x2, [x1]
+        cbnz    w0, 1b
+        ret
+ENDPROC(\name   )
+        .endm
+
+        .macro  testop, name, instr
+ENTRY(  \name   )
+        and     x3, x0, #63             // Get bit offset
+        eor     x0, x0, x3              // Clear low bits
+        mov     x2, #1
+        add     x1, x1, x0, lsr #3      // Get word offset
+        lsl     x4, x2, x3              // Create mask
+        smp_dmb ish
+1:      ldxr    x2, [x1]
+        lsr     x0, x2, x3              // Save old value of bit
+        \instr  x2, x2, x4              // toggle bit
+        stxr    w2, x2, [x1]
+        cbnz    w2, 1b
+        smp_dmb ish
+        and     x0, x0, #1
+3:      ret
+ENDPROC(\name   )
+        .endm
+
+/*
+ * Atomic bit operations.
+ */
+        bitop   change_bit, eor
+        bitop   clear_bit, bic
+        bitop   set_bit, orr
+
+        testop  test_and_change_bit, eor
+        testop  test_and_clear_bit, bic
+        testop  test_and_set_bit, orr
diff --git a/arch/arm64/lib/bitops.c b/arch/arm64/lib/bitops.c
deleted file mode 100644
index aa4965e60acc..000000000000
--- a/arch/arm64/lib/bitops.c
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
- * Copyright (C) 2012 ARM Limited
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#include <linux/kernel.h>
-#include <linux/spinlock.h>
-#include <linux/atomic.h>
-
-#ifdef CONFIG_SMP
-arch_spinlock_t __atomic_hash[ATOMIC_HASH_SIZE] __lock_aligned = {
-       [0 ... (ATOMIC_HASH_SIZE-1)]  = __ARCH_SPIN_LOCK_UNLOCKED
-};
-#endif