asm-generic: ticket-lock: New generic ticket-based spinlock

This is a simple, fair spinlock.  Specifically it doesn't have all the
subtle memory model dependencies that qspinlock has, which makes it more
suitable for simple systems as it is more likely to be correct.  It is
implemented entirely in terms of standard atomics and thus works fine
without any arch-specific code.

This replaces the existing asm-generic/spinlock.h, which just errored
out on SMP systems.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/asm-generic/spinlock_types.h b/include/asm-generic/spinlock_types.h
new file mode 100644
index 000000000000..8962bb730945
--- /dev/null
+++ b/include/asm-generic/spinlock_types.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_GENERIC_SPINLOCK_TYPES_H
+#define __ASM_GENERIC_SPINLOCK_TYPES_H
+
+#include <linux/types.h>
+typedef atomic_t arch_spinlock_t;
+
+/*
+ * qrwlock_types depends on arch_spinlock_t, so we must typedef that before the
+ * include.
+ */
+#include <asm/qrwlock_types.h>
+
+#define __ARCH_SPIN_LOCK_UNLOCKED	ATOMIC_INIT(0)
+
+#endif /* __ASM_GENERIC_SPINLOCK_TYPES_H */