Re: [PATCH 2/4] RISC-V: don't parse dt isa string to get rv32/rv64

Andrew Jones
2023-04-26T09:37:55Z

On Mon, Apr 24, 2023 at 09:49:09PM +0200, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@vrull.eu>
>
> When filling hwcap the kernel already expects the isa string to start with
> rv32 if CONFIG_32BIT and rv64 if CONFIG_64BIT.
>
> So when recreating the runtime isa-string we can also just go the other way
> to get the correct starting point for it.
>
> Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> ---
> arch/riscv/kernel/cpu.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index ebc478f0a16c..06c2f587a176 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -244,7 +244,7 @@ static void strcat_isa_ext(char *isa_str)
> */
> static const char base_riscv_exts[13] = "imafdqcbkjpvh";
>
> -static char *riscv_create_isa_string(const char *isa)
> +static char *riscv_create_isa_string(void)
> {
> int maxlen = 4;
> char *isa_str;
> @@ -261,7 +261,11 @@ static char *riscv_create_isa_string(const char *isa)
> return ERR_PTR(-ENOMEM);
>
> /* Print the rv[64/32] part */
> - strncat(isa_str, isa, 4);
> +#if IS_ENABLED(CONFIG_32BIT)
> + strncat(isa_str, "rv32", 4);
> +#elif IS_ENABLED(CONFIG_64BIT)
> + strncat(isa_str, "rv64", 4);
> +#endif

I see we do the validation in riscv_fill_hwcap() and we also do this
#ifdeffery there, but I can't see any reason not to do

if (IS_ENABLED(CONFIG_32BIT))
...
else
...

instead.

>
> for (i = 0; i < sizeof(base_riscv_exts); i++) {
> if (__riscv_isa_extension_available(NULL, base_riscv_exts[i] - 'a'))
> @@ -280,7 +284,7 @@ static void print_isa(struct seq_file *f, const char *isa)
>
> seq_puts(f, "isa\t\t: ");
>
> - isa_str = riscv_create_isa_string(isa);
> + isa_str = riscv_create_isa_string();

Why are we still passing 'isa' to print_isa()? It's now unused and
print_isa()'s single caller only fetches it from the DT for this
one purpose, so that of_property_read_string() call could now also
be dropped.

> if (!IS_ERR(isa_str)) {
> seq_write(f, isa_str, strlen(isa_str));
> kfree(isa_str);
> --
> 2.39.0
>

Thanks,
drew