Re: [PATCH v4 4/6] RISC-V: Implement multi-letter ISA extension probing framework

["Heiko Stübner" <heiko@sntech.de>]

Am Mittwoch, 16. Februar 2022, 01:29:09 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@rivosinc.com>

With my in-flight svpbmt series:
Tested-by: Heiko Stuebner <heiko@sntech.de>

> ---
>  arch/riscv/include/asm/hwcap.h | 18 ++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c | 24 ++++++++++++++++++------
>  2 files changed, 36 insertions(+), 6 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 cd9eb34f8d11..59c70c104256 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;
> +		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
>  
>  		if (riscv_of_processor_hartid(node) < 0)
>  			continue;
> @@ -100,6 +100,7 @@ void __init riscv_fill_hwcap(void)
>  		if (!strncmp(isa, "rv64", 4))
>  			isa += 4;
>  #endif
> +		bitmap_zero(this_isa, RISCV_ISA_EXT_MAX);
>  		for (; *isa; ++isa) {
>  			const char *ext = isa++;
>  			const char *ext_end = isa;
> @@ -167,12 +168,22 @@ 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)) {    \
> +					set_bit(bit, this_isa);			\
> +					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'));
> +				set_bit(*ext - 'a', this_isa);
>  			}
> +#undef SET_ISA_EXT_MAP
>  		}
>  
>  		/*
> @@ -185,10 +196,11 @@ void __init riscv_fill_hwcap(void)
>  		else
>  			elf_hwcap = this_hwcap;
>  
> -		if (riscv_isa[0])
> -			riscv_isa[0] &= this_isa;
> +		if (bitmap_weight(riscv_isa, RISCV_ISA_EXT_MAX))
> +			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
>  		else
> -			riscv_isa[0] = this_isa;
> +			bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
> +
>  	}
>  
>  	/* We don't support systems with F but without D, so mask those out
> @@ -202,7 +214,7 @@ void __init riscv_fill_hwcap(void)
>  	for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
>  		if (riscv_isa[0] & BIT_MASK(i))
>  			print_str[j++] = (char)('a' + i);
> -	pr_info("riscv: ISA extensions %s\n", print_str);
> +	pr_info("riscv: base ISA extensions %s\n", print_str);
>  
>  	memset(print_str, 0, sizeof(print_str));
>  	for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
>