Re: [PATCH v2 13/13] RISC-V: add zbb support to string functions

From: Conor Dooley <conor@kernel.org>
To: Heiko Stuebner <heiko@sntech.de>
Cc: linux-riscv@lists.infradead.org, palmer@dabbelt.com,
	christoph.muellner@vrull.eu, prabhakar.csengg@gmail.com,
	philipp.tomsich@vrull.eu, ajones@ventanamicro.com,
	emil.renner.berthing@canonical.com,
	Heiko Stuebner <heiko.stuebner@vrull.eu>
Subject: Re: [PATCH v2 13/13] RISC-V: add zbb support to string functions
Date: Wed, 30 Nov 2022 16:53:41 +0000	[thread overview]
Message-ID: <Y4eKlYlUOE2uGaxH@spud> (raw)
In-Reply-To: <20221128102632.435174-14-heiko@sntech.de>

On Mon, Nov 28, 2022 at 11:26:32AM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> 
> Add handling for ZBB extension and add support for using it as a
> variant for optimized string functions.
> 
> Co-developed-by: Christoph Muellner <christoph.muellner@vrull.eu>
> Signed-off-by: Christoph Muellner <christoph.muellner@vrull.eu>
> Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> ---

> diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> index 4180312d2a70..95e626b7281e 100644
> --- a/arch/riscv/include/asm/errata_list.h
> +++ b/arch/riscv/include/asm/errata_list.h
> @@ -24,7 +24,8 @@
>  
>  #define	CPUFEATURE_SVPBMT 0
>  #define	CPUFEATURE_ZICBOM 1
> -#define	CPUFEATURE_NUMBER 2
> +#define	CPUFEATURE_ZBB 2

I was going to complain that you did not align these but none of the
other "errata" are /shrug

> +#define	CPUFEATURE_NUMBER 3
>  
>  #ifdef __ASSEMBLY__
>  
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index b22525290073..ac5555fd9788 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -59,6 +59,7 @@ enum riscv_isa_ext_id {
>  	RISCV_ISA_EXT_ZIHINTPAUSE,
>  	RISCV_ISA_EXT_SSTC,
>  	RISCV_ISA_EXT_SVINVAL,
> +	RISCV_ISA_EXT_ZBB,

I'll avoid commenting on this for now haha. I've caused enough havoc.

>  	RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
>  };
>  

> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index bf9dd6764bad..95d1b8d74342 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -162,6 +162,7 @@ arch_initcall(riscv_cpuinfo_init);
>   *    extensions by an underscore.
>   */
>  static struct riscv_isa_ext_data isa_ext_arr[] = {
> +	__RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
>  	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
>  	__RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
>  	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index ba62a4ff5ccd..2ec60794293f 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -199,6 +199,7 @@ void __init riscv_fill_hwcap(void)
>  				this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
>  				set_bit(*ext - 'a', this_isa);
>  			} else {
> +				SET_ISA_EXT_MAP("zbb", RISCV_ISA_EXT_ZBB);
>  				SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
>  				SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
>  				SET_ISA_EXT_MAP("zicbom", RISCV_ISA_EXT_ZICBOM);

This all looks fair, and since I was happy with it matching the
"reference" implementation in the spec doc etc last time & you've
cleaned up the readability bits & bobs:
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.

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