linux-kernel - Re: [PATCH 2/5] riscv: Add QUEUED_SPINLOCKS & QUEUED

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Date:   Tue, 24 Nov 2020 15:39:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     guoren@...nel.org
Cc:     arnd@...db.de, palmerdabbelt@...gle.com, paul.walmsley@...ive.com,
        anup@...infault.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-csky@...r.kernel.org,
        Guo Ren <guoren@...ux.alibaba.com>,
        Michael Clark <michaeljclark@....com>
Subject: Re: [PATCH 2/5] riscv: Add QUEUED_SPINLOCKS & QUEUED_RWLOCKS
 supported

On Tue, Nov 24, 2020 at 01:43:54PM +0000, guoren@...nel.org wrote:
> diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
> index 59dd7be..6f5f438 100644
> --- a/arch/riscv/include/asm/Kbuild
> +++ b/arch/riscv/include/asm/Kbuild
> @@ -6,3 +6,6 @@ generic-y += kvm_para.h
>  generic-y += local64.h
>  generic-y += user.h
>  generic-y += vmlinux.lds.h
> +generic-y += mcs_spinlock.h
> +generic-y += qrwlock.h
> +generic-y += qspinlock.h
> diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> index 5609185..e178700 100644
> --- a/arch/riscv/include/asm/cmpxchg.h
> +++ b/arch/riscv/include/asm/cmpxchg.h
> @@ -16,7 +16,43 @@
>  	__typeof__(ptr) __ptr = (ptr);					\
>  	__typeof__(new) __new = (new);					\
>  	__typeof__(*(ptr)) __ret;					\
> +	register unsigned long __rc, tmp, align, addr;			\
>  	switch (size) {							\
> +	case 2:								\
> +		align = ((unsigned long) __ptr & 0x3);			\
> +		addr = ((unsigned long) __ptr & ~0x3);			\
> +		if (align) {						\
> +		__asm__ __volatile__ (					\
> +			"0:	lr.w %0, 0(%z4)\n"			\
> +			"	move %1, %0\n"				\
> +			"	slli %1, %1, 16\n"			\
> +			"	srli %1, %1, 16\n"			\
> +			"	move %2, %z3\n"				\
> +			"	slli %2, %2, 16\n"			\
> +			"	or   %1, %2, %1\n"			\
> +			"	sc.w %2, %1, 0(%z4)\n"			\
> +			"	bnez %2, 0b\n"				\
> +			"	srli %0, %0, 16\n"			\
> +			: "=&r" (__ret), "=&r" (tmp), "=&r" (__rc)	\
> +			: "rJ" (__new), "rJ"(addr)			\
> +			: "memory");					\
> +		} else {						\
> +		__asm__ __volatile__ (					\
> +			"0:	lr.w %0, (%z4)\n"			\
> +			"	move %1, %0\n"				\
> +			"	srli %1, %1, 16\n"			\
> +			"	slli %1, %1, 16\n"			\
> +			"	move %2, %z3\n"				\
> +			"	or   %1, %2, %1\n"			\
> +			"	sc.w %2, %1, 0(%z4)\n"			\
> +			"	bnez %2, 0b\n"				\
> +			"	slli %0, %0, 16\n"			\
> +			"	srli %0, %0, 16\n"			\
> +			: "=&r" (__ret), "=&r" (tmp), "=&r" (__rc)	\
> +			: "rJ" (__new), "rJ"(addr)			\
> +			: "memory");					\
> +		}							\
> +		break;							\
>  	case 4:								\
>  		__asm__ __volatile__ (					\
>  			"	amoswap.w %0, %2, %1\n"			\

I'm pretty sure there's a handfull of implementations like this out
there... if only we could share.

Anyway, this too should be an independent patch.