Re: [PATCH 1/4] RISC-V: create ISA string separately - not as part of cpuinfo

[Andrew Jones]

On Mon, Apr 24, 2023 at 09:49:08PM +0200, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> 
> The isa string is a very central part of the RISC-V architecture, so will
> be needed in other places as well.
> 
> So in a first step decouple the generation of the runtime isa-string from
> /proc/cpuinfo - its current only user.
> 
> The resulting string should not differ from the previously generated one.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> ---
>  arch/riscv/kernel/cpu.c | 70 ++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 62 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 3df38052dcbd..ebc478f0a16c 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -193,10 +193,33 @@ static struct riscv_isa_ext_data isa_ext_arr[] = {
>  	__RISCV_ISA_EXT_DATA("", RISCV_ISA_EXT_MAX),
>  };
>  
> -static void print_isa_ext(struct seq_file *f)
> +static int strlen_isa_ext(void)
>  {
>  	struct riscv_isa_ext_data *edata;
> -	int i = 0, arr_sz;
> +	int ext_len = 0, i, arr_sz;
> +
> +	arr_sz = ARRAY_SIZE(isa_ext_arr) - 1;

I see this subtracting of 1 here and then using <= below comes from
the current print_isa_ext(), but it seems odd. How about just

static int strlen_isa_ext(void)
{
   int ext_len = 0;

   for (int i = 0; i < ARRAY_SIZE(isa_ext_arr); ++i) {
      struct riscv_isa_ext_data *edata = &isa_ext_arr[i];
      ...
   }

   return ext_len;
}

> +
> +	/* No extension support available */
> +	if (arr_sz <= 0)
> +		return 0;
> +
> +	for (i = 0; i <= arr_sz; i++) {
> +		edata = &isa_ext_arr[i];
> +		if (!__riscv_isa_extension_available(NULL, edata->isa_ext_id))
> +			continue;
> +
> +		/* string length + underscore */
> +		ext_len += strlen(edata->uprop) + 1;
> +	}
> +
> +	return ext_len;
> +}
> +
> +static void strcat_isa_ext(char *isa_str)
> +{
> +	struct riscv_isa_ext_data *edata;
> +	int i, arr_sz;
>  
>  	arr_sz = ARRAY_SIZE(isa_ext_arr) - 1;
>  
> @@ -208,7 +231,8 @@ static void print_isa_ext(struct seq_file *f)
>  		edata = &isa_ext_arr[i];
>  		if (!__riscv_isa_extension_available(NULL, edata->isa_ext_id))
>  			continue;
> -		seq_printf(f, "_%s", edata->uprop);
> +		strcat(isa_str, "_");
> +		strcat(isa_str, edata->uprop);
>  	}
>  }
>  
> @@ -220,19 +244,49 @@ static void print_isa_ext(struct seq_file *f)
>   */
>  static const char base_riscv_exts[13] = "imafdqcbkjpvh";
>  
> -static void print_isa(struct seq_file *f, const char *isa)
> +static char *riscv_create_isa_string(const char *isa)
>  {
> +	int maxlen = 4;
> +	char *isa_str;
>  	int i;
>  
> -	seq_puts(f, "isa\t\t: ");
> +	/* calculate the needed string length */
> +	for (i = 0; i < sizeof(base_riscv_exts); i++)
> +		if (__riscv_isa_extension_available(NULL, base_riscv_exts[i] - 'a'))
> +			maxlen++;
> +	maxlen += strlen_isa_ext();
> +
> +	isa_str = kzalloc(maxlen, GFP_KERNEL);
> +	if (!isa_str)
> +		return ERR_PTR(-ENOMEM);
> +
>  	/* Print the rv[64/32] part */
> -	seq_write(f, isa, 4);
> +	strncat(isa_str, isa, 4);
> +
>  	for (i = 0; i < sizeof(base_riscv_exts); i++) {
>  		if (__riscv_isa_extension_available(NULL, base_riscv_exts[i] - 'a'))
>  			/* Print only enabled the base ISA extensions */
> -			seq_write(f, &base_riscv_exts[i], 1);
> +			strncat(isa_str, &base_riscv_exts[i], 1);
> +	}
> +
> +	strcat_isa_ext(isa_str);
> +
> +	return isa_str;
> +}
> +
> +static void print_isa(struct seq_file *f, const char *isa)
> +{
> +	char *isa_str;
> +
> +	seq_puts(f, "isa\t\t: ");
> +
> +	isa_str = riscv_create_isa_string(isa);
> +	if (!IS_ERR(isa_str)) {
> +		seq_write(f, isa_str, strlen(isa_str));
> +		kfree(isa_str);
> +	} else {
> +		seq_puts(f, "unknown");
>  	}
> -	print_isa_ext(f);
>  	seq_puts(f, "\n");
>  }
>  
> -- 
> 2.39.0

Otherwise,

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>