linux-kernel - Re: [PATCH v2 4/6] RISC-V: Implement multi-letter ISA extension probing framework

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Message-ID: <3881365.IPMWXPQfj1@diego>
Date:   Mon, 14 Feb 2022 21:05:59 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Cc:     Atish Patra <atishp@...osinc.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atishp@...shpatra.org>,
        Anup Patel <anup@...infault.org>,
        Damien Le Moal <damien.lemoal@....com>,
        devicetree@...r.kernel.org, Jisheng Zhang <jszhang@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Atish Patra <atishp@...osinc.com>
Subject: Re: [PATCH v2 4/6] RISC-V: Implement multi-letter ISA extension probing framework

Am Donnerstag, 10. Februar 2022, 22:40:16 CET schrieb Atish Patra:
> Multi-letter extensions can be probed using exising
> riscv_isa_extension_available API now. It doesn't support versioning
> right now as there is no use case for it.
> Individual extension specific implementation will be added during
> each extension support.
> 
> Signed-off-by: Atish Patra <atishp@...osinc.com>

Tested-by: Heiko Stuebner <heiko@...ech.de>


By the way, does a similar parsing exist for opensbi as well?
Things like svpbmt as well as zicbom have CSR bits controlling how
these functions should behave (enabling them, etc), so I guess
opensbi also needs to parse the extensions from the ISA string?


Heiko

> ---
>  arch/riscv/include/asm/hwcap.h | 18 ++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c | 27 ++++++++++++++++++++++++---
>  2 files changed, 42 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 5ce50468aff1..170bd80da520 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -34,7 +34,25 @@ extern unsigned long elf_hwcap;
>  #define RISCV_ISA_EXT_s		('s' - 'a')
>  #define RISCV_ISA_EXT_u		('u' - 'a')
>  
> +/*
> + * Increse this to higher value as kernel support more ISA extensions.
> + */
>  #define RISCV_ISA_EXT_MAX	64
> +#define RISCV_ISA_EXT_NAME_LEN_MAX 32
> +
> +/* The base ID for multi-letter ISA extensions */
> +#define RISCV_ISA_EXT_BASE 26
> +
> +/*
> + * This enum represent the logical ID for each multi-letter RISC-V ISA extension.
> + * The logical ID should start from RISCV_ISA_EXT_BASE and must not exceed
> + * RISCV_ISA_EXT_MAX. 0-25 range is reserved for single letter
> + * extensions while all the multi-letter extensions should define the next
> + * available logical extension id.
> + */
> +enum riscv_isa_ext_id {
> +	RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
> +};
>  
>  unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
>  
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index e9e3b0693d16..469b9739faf7 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -83,7 +83,7 @@ void __init riscv_fill_hwcap(void)
>  
>  	for_each_of_cpu_node(node) {
>  		unsigned long this_hwcap = 0;
> -		unsigned long this_isa = 0;
> +		uint64_t this_isa = 0;
>  
>  		if (riscv_of_processor_hartid(node) < 0)
>  			continue;
> @@ -169,12 +169,22 @@ void __init riscv_fill_hwcap(void)
>  			if (*isa != '_')
>  				--isa;
>  
> +#define SET_ISA_EXT_MAP(name, bit)						\
> +			do {							\
> +				if ((ext_end - ext == sizeof(name) - 1) &&	\
> +				     !memcmp(ext, name, sizeof(name) - 1)) {    \
> +					this_isa |= (1UL << bit);		\
> +					pr_info("Found ISA extension %s", name);\
> +				}						\
> +			} while (false)						\
> +
>  			if (unlikely(ext_err))
>  				continue;
>  			if (!ext_long) {
>  				this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
>  				this_isa |= (1UL << (*ext - 'a'));
>  			}
> +#undef SET_ISA_EXT_MAP
>  		}
>  
>  		/*
> @@ -187,10 +197,21 @@ void __init riscv_fill_hwcap(void)
>  		else
>  			elf_hwcap = this_hwcap;
>  
> -		if (riscv_isa[0])
> +		if (riscv_isa[0]) {
> +#if IS_ENABLED(CONFIG_32BIT)
> +			riscv_isa[0] &= this_isa & 0xFFFFFFFF;
> +			riscv_isa[1] &= this_isa >> 32;
> +#else
>  			riscv_isa[0] &= this_isa;
> -		else
> +#endif
> +		} else {
> +#if IS_ENABLED(CONFIG_32BIT)
> +			riscv_isa[0] = this_isa & 0xFFFFFFFF;
> +			riscv_isa[1] = this_isa >> 32;
> +#else
>  			riscv_isa[0] = this_isa;
> +#endif
> +		}
>  	}
>  
>  	/* We don't support systems with F but without D, so mask those out
>