Re: [PATCH v1 8/9] RISC-V: enable extension detection from new properties

[Andrew Jones]

On Mon, Jun 26, 2023 at 12:19:46PM +0100, Conor Dooley wrote:
> Add support for parsing the new riscv,isa-extensions property in
> riscv_fill_hwcap(), by means of a new "property" member of the
> riscv_isa_ext_data struct. For now, this shadows the name of the
> extension, however this may not be the case for all extensions.
> For the sake of backwards compatibility, fall back to the old scheme
> if the new properties are not detected. For now, just inform, rather
> than warn, when that happens.
> 
> Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> ---
> Naming things is hard, didn't know what to call the new function...

riscv_fill_hwcap_from_isa_extensions() ?

_new() won't age well.

> ---
>  arch/riscv/include/asm/hwcap.h |  1 +
>  arch/riscv/kernel/cpufeature.c | 80 ++++++++++++++++++++++++++++++----
>  2 files changed, 72 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 6ad896dc4342..e7f235868aa2 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -77,6 +77,7 @@ unsigned long riscv_get_elf_hwcap(void);
>  struct riscv_isa_ext_data {
>  	const unsigned int id;
>  	const char *name;
> +	const char *property;
>  	const bool multi_letter;
>  };
>  
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 366477ba1eea..72eb757ad871 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -101,6 +101,7 @@ static bool riscv_isa_extension_check(int id)
>  
>  #define __RISCV_ISA_EXT_DATA(_name, _id, _multi) {	\
>  	.name = #_name,					\
> +	.property = #_name,				\
>  	.id = _id,					\
>  	.multi_letter = _multi,				\
>  }
> @@ -416,16 +417,66 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
>  		acpi_put_table((struct acpi_table_header *)rhct);
>  }
>  
> +static int __init riscv_fill_hwcap_new(unsigned long *isa2hwcap)
> +{
> +	unsigned int cpu;
> +
> +	for_each_possible_cpu(cpu) {
> +		unsigned long this_hwcap = 0;
> +		struct device_node *cpu_node;
> +		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
> +
> +		cpu_node = of_cpu_device_node_get(cpu);
> +		if (!cpu_node) {
> +			pr_warn("Unable to find cpu node\n");
> +			continue;
> +		}
> +
> +		if (!of_property_present(cpu_node, "riscv,isa-extensions"))
> +			continue;
> +
> +		for (int i = 0; i < riscv_isa_ext_count; i++) {
> +			if (of_property_match_string(cpu_node, "riscv,isa-extensions",
> +						     riscv_isa_ext[i].name) < 0)
> +				continue;
> +
> +			if (!riscv_isa_extension_check(riscv_isa_ext[i].id))
> +				continue;
> +
> +			if (!riscv_isa_ext[i].multi_letter)
> +				this_hwcap |= isa2hwcap[riscv_isa_ext[i].id];
> +
> +			set_bit(riscv_isa_ext[i].id, this_isa);
> +		}
> +
> +		of_node_put(cpu_node);
> +
> +		/*
> +		 * All "okay" harts should have same isa. Set HWCAP based on
> +		 * common capabilities of every "okay" hart, in case they don't.
> +		 */
> +		if (elf_hwcap)
> +			elf_hwcap &= this_hwcap;
> +		else
> +			elf_hwcap = this_hwcap;
> +
> +		if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
> +			bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
> +		else
> +			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
> +	}
> +
> +	if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
> +		return -ENOENT;
> +
> +	return 0;
> +}
> +
>  void __init riscv_fill_hwcap(void)
>  {
> -	struct device_node *node;
> -	const char *isa;
>  	char print_str[NUM_ALPHA_EXTS + 1];
> -	int i, j, rc;
>  	unsigned long isa2hwcap[26] = {0};
> -	struct acpi_table_header *rhct;
> -	acpi_status status;
> -	unsigned int cpu;
> +	int i, j;
>  
>  	isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
>  	isa2hwcap['m' - 'a'] = COMPAT_HWCAP_ISA_M;
> @@ -435,10 +486,21 @@ void __init riscv_fill_hwcap(void)
>  	isa2hwcap['c' - 'a'] = COMPAT_HWCAP_ISA_C;
>  	isa2hwcap['v' - 'a'] = COMPAT_HWCAP_ISA_V;
>  
> -	riscv_fill_hwcap_from_isa_string(isa2hwcap);
> +	if (!acpi_disabled) {
> +		riscv_fill_hwcap_from_isa_string(isa2hwcap);
> +	} else {
> +		int ret = riscv_fill_hwcap_new(isa2hwcap);
>  
> -	/* We don't support systems with F but without D, so mask those out
> -	 * here. */
> +		if (ret) {
> +			pr_info("Falling back to deprecated \"riscv,isa\"\n");
> +			riscv_fill_hwcap_from_isa_string(isa2hwcap);
> +		}
> +	}
> +
> +	/*
> +	 * We don't support systems with F but without D, so mask those out
> +	 * here.
> +	 */
>  	if ((elf_hwcap & COMPAT_HWCAP_ISA_F) && !(elf_hwcap & COMPAT_HWCAP_ISA_D)) {
>  		pr_info("This kernel does not support systems with F but not D\n");
>  		elf_hwcap &= ~COMPAT_HWCAP_ISA_F;
> -- 
> 2.40.1
>

Other than the name and moving the removal of the unused declarations to
the previous patch,

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>

Thanks,
drew