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SubjectRe: [PATCH v2 2/5] riscv: Add checksum library
On Tue, Sep 05, 2023 at 09:46:51PM -0700, Charlie Jenkins wrote:

> +#ifdef CONFIG_RISCV_ISA_ZBB
> + if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> + /*
> + * Zbb is likely available when the kernel is compiled with Zbb
> + * support, so nop when Zbb is available and jump when Zbb is
> + * not available.
> + */
> + asm_volatile_goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
> + RISCV_ISA_EXT_ZBB, 1)
> + :
> + :
> + :
> + : no_zbb);
> + } else {
> + if (!__riscv_isa_extension_available(NULL, RISCV_ISA_EXT_ZBB))
> + goto no_zbb;
> + }

Again, do these constructs have an appreciable benefit over doing
if (!riscv_has_extension_likely(<ZBB>)
goto no_zbb;

?

That encaspulates the fallback to a non-alternative mechanism for you,
in case you had not noticed.
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