Re: [PATCH v2 06/10] riscv: Implement xchg8/16() using Zabha

From: Andrea Parri <parri.andrea@gmail.com>
To: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Nathan Chancellor <nathan@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
	Waiman Long <longman@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>, Arnd Bergmann <arnd@arndb.de>,
	Leonardo Bras <leobras@redhat.com>, Guo Ren <guoren@kernel.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH v2 06/10] riscv: Implement xchg8/16() using Zabha
Date: Thu, 27 Jun 2024 15:45:47 +0200	[thread overview]
Message-ID: <Zn1tC1G6eiyIW/yJ@andrea> (raw)
In-Reply-To: <20240626130347.520750-7-alexghiti@rivosinc.com>

> -#define __arch_xchg_masked(sc_sfx, prepend, append, r, p, n)		\
> +#define __arch_xchg_masked(sc_sfx, swap_sfx, prepend, sc_append,	\
> +			   swap_append, r, p, n)			\
>  ({									\
> +	__label__ zabha, end;						\
> +									\
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) {			\
> +		asm goto(ALTERNATIVE("nop", "j %[zabha]", 0,		\
> +				     RISCV_ISA_EXT_ZABHA, 1)		\
> +			 : : : : zabha);				\
> +	}								\
> +									\
>  	u32 *__ptr32b = (u32 *)((ulong)(p) & ~0x3);			\
>  	ulong __s = ((ulong)(p) & (0x4 - sizeof(*p))) * BITS_PER_BYTE;	\
>  	ulong __mask = GENMASK(((sizeof(*p)) * BITS_PER_BYTE) - 1, 0)	\
> @@ -28,12 +37,25 @@
>  	       "	or   %1, %1, %z3\n"				\
>  	       "	sc.w" sc_sfx " %1, %1, %2\n"			\
>  	       "	bnez %1, 0b\n"					\
> -	       append							\
> +	       sc_append							\
>  	       : "=&r" (__retx), "=&r" (__rc), "+A" (*(__ptr32b))	\
>  	       : "rJ" (__newx), "rJ" (~__mask)				\
>  	       : "memory");						\
>  									\
>  	r = (__typeof__(*(p)))((__retx & __mask) >> __s);		\
> +	goto end;							\
> +									\
> +zabha:									\
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) {			\
> +		__asm__ __volatile__ (					\
> +			prepend						\
> +			"	amoswap" swap_sfx " %0, %z2, %1\n"	\
> +			swap_append						\
> +			: "=&r" (r), "+A" (*(p))			\
> +			: "rJ" (n)					\
> +			: "memory");					\
> +	}								\
> +end:;									\
>  })

As for patch #1: why the semicolon? and should the second IS_ENABLED()
be kept?

> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index e17d0078a651..f71ddd2ca163 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -81,6 +81,7 @@
>  #define RISCV_ISA_EXT_ZTSO		72
>  #define RISCV_ISA_EXT_ZACAS		73
>  #define RISCV_ISA_EXT_XANDESPMU		74
> +#define RISCV_ISA_EXT_ZABHA		75
>  
>  #define RISCV_ISA_EXT_XLINUXENVCFG	127
>  
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 5ef48cb20ee1..c125d82c894b 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -257,6 +257,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
>  	__RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
>  	__RISCV_ISA_EXT_DATA(zacas, RISCV_ISA_EXT_ZACAS),
> +	__RISCV_ISA_EXT_DATA(zabha, RISCV_ISA_EXT_ZABHA),
>  	__RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
>  	__RISCV_ISA_EXT_DATA(zfh, RISCV_ISA_EXT_ZFH),
>  	__RISCV_ISA_EXT_DATA(zfhmin, RISCV_ISA_EXT_ZFHMIN),

To be squashed into patch #3?

  Andrea