lib: sbi: Replace test-and-set locks by ticket locks

Replace the test-and-set spinlock implementation with ticket locks
in order to get fairness (in form of FIFO order).

The implementation uses a 32-bit wide struct, which consists of
two 16-bit counters (owner and next). This is inspired by similar
spinlock implementations on other architectures.
This allows that the code works for both, RV32 and RV64.

Signed-off-by: Christoph Muellner <cmuellner@linux.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Xiang W <wxjstz@126.com>

1 files changed, 22 insertions, 11 deletions

diff --git a/include/sbi/riscv_locks.h b/include/sbi/riscv_locks.h
index faa9676..492935f 100644
--- a/include/sbi/riscv_locks.h
+++ b/include/sbi/riscv_locks.h
@@ -2,26 +2,37 @@
  * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright (c) 2019 Western Digital Corporation or its affiliates.
- *
- * Authors:
- *   Anup Patel <anup.patel@wdc.com>
+ * Copyright (c) 2021 Christoph Müllner <cmuellner@linux.com>
  */
 
 #ifndef __RISCV_LOCKS_H__
 #define __RISCV_LOCKS_H__
 
+#include <sbi/sbi_types.h>
+
+#define TICKET_SHIFT	16
+
 typedef struct {
-	volatile long lock;
-} spinlock_t;
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+       u16 next;
+       u16 owner;
+#else
+       u16 owner;
+       u16 next;
+#endif
+} __aligned(4) spinlock_t;
+
+#define __SPIN_LOCK_UNLOCKED	\
+	(spinlock_t) { 0, 0 }
 
-#define __RISCV_SPIN_UNLOCKED 0
+#define SPIN_LOCK_INIT(x)	\
+	x = __SPIN_LOCK_UNLOCKED
 
-#define SPIN_LOCK_INIT(x) (x).lock = __RISCV_SPIN_UNLOCKED
+#define SPIN_LOCK_INITIALIZER	\
+	__SPIN_LOCK_UNLOCKED
 
-#define SPIN_LOCK_INITIALIZER                  \
-	{                                      \
-		.lock = __RISCV_SPIN_UNLOCKED, \
-	}
+#define DEFINE_SPIN_LOCK(x)	\
+	spinlock_t SPIN_LOCK_INIT(x)
 
 int spin_lock_check(spinlock_t *lock);