csky: Add qspinlock support

Enable qspinlock by the requirements mentioned in a8ad07e5240c9
("asm-generic: qspinlock: Indicate the use of mixed-size atomics").

C-SKY only has "ldex/stex" for all atomic operations. So csky give a
strong forward guarantee for "ldex/stex." That means when ldex grabbed
the cache line into $L1, it would block other cores from snooping the
address with several cycles. The atomic_fetch_add & xchg16 has the same
forward guarantee level in C-SKY.

Qspinlock has better code size and performance in a fast path.

Signed-off-by: Guo Ren <[e-mail]>
Signed-off-by: Guo Ren <[e-mail]>

arch/csky/Kconfig

···
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_QUEUED_RWLOCKS
+	select ARCH_USE_QUEUED_SPINLOCKS
 	select ARCH_WANT_FRAME_POINTERS if !CPU_CK610 && $(cc-option,-mbacktrace)
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select COMMON_CLK

arch/csky/include/asm/Kbuild

···
 generic-y += extable.h
 generic-y += gpio.h
 generic-y += kvm_para.h
-generic-y += spinlock.h
-generic-y += spinlock_types.h
+generic-y += mcs_spinlock.h
 generic-y += qrwlock.h
 generic-y += qrwlock_types.h
+generic-y += qspinlock.h
 generic-y += parport.h
 generic-y += user.h
 generic-y += vmlinux.lds.h

arch/csky/include/asm/cmpxchg.h

···
 	__typeof__(*(ptr)) __ret;				\
 	unsigned long tmp;					\
 	switch (size) {						\
+	case 2: {						\
+		u32 ret;					\
+		u32 shif = ((ulong)__ptr & 2) ? 16 : 0;		\
+		u32 mask = 0xffff << shif;			\
+		__ptr = (__typeof__(ptr))((ulong)__ptr & ~2);	\
+		__asm__ __volatile__ (				\
+			"1:	ldex.w %0, (%4)\n"		\
+			"	and    %1, %0, %2\n"		\
+			"	or     %1, %1, %3\n"		\
+			"	stex.w %1, (%4)\n"		\
+			"	bez    %1, 1b\n"		\
+			: "=&r" (ret), "=&r" (tmp)		\
+			: "r" (~mask),				\
+			  "r" ((u32)__new << shif),		\
+			  "r" (__ptr)				\
+			: "memory");				\
+		__ret = (__typeof__(*(ptr)))			\
+			((ret & mask) >> shif);			\
+		break;						\
+	}							\
 	case 4:							\
 		asm volatile (					\
 		"1:	ldex.w		%0, (%3) \n"		\

arch/csky/include/asm/spinlock.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_CSKY_SPINLOCK_H
+#define __ASM_CSKY_SPINLOCK_H
+
+#include <asm/qspinlock.h>
+#include <asm/qrwlock.h>
+
+/* See include/linux/spinlock.h */
+#define smp_mb__after_spinlock()	smp_mb()
+
+#endif /* __ASM_CSKY_SPINLOCK_H */

arch/csky/include/asm/spinlock_types.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_CSKY_SPINLOCK_TYPES_H
+#define __ASM_CSKY_SPINLOCK_TYPES_H
+
+#include <asm-generic/qspinlock_types.h>
+#include <asm-generic/qrwlock_types.h>
+
+#endif /* __ASM_CSKY_SPINLOCK_TYPES_H */