[PATCH v3 2/2] riscv: accept the atomic extensions this kernel was built with

[Conor Dooley]

On Mon, Oct 26, 2026 at 11:20:03AM +0200, Vladimir Kondratiev wrote:
> riscv_early_of_processor_hartid() rejects a hart unless its
> riscv,isa-extensions property contains "a". That rejects a Zalrsc-only
> hart even when the kernel was built to use only LR/SC.
> 
> Require "a" or "zaamo" when the kernel emits AMO, and "a" or "zalrsc"
> when it emits LR/SC. A normal build defines both toolchain macros and
> still requires the full A extension. The legacy "riscv,isa" fallback
> keeps its rv{32,64}ima check.
> 
> Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev at mobileye.com
>

IMO, this should not be a separate patch.

> ---
>  arch/riscv/kernel/cpu.c | 28 ++++++++++++++++++++++++----
>  1 file changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 3dbc8cc557dd..5d1e39d16e59 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -82,12 +82,32 @@ int __init riscv_early_of_processor_hartid(struct device_node *node, unsigned lo
>  		return -ENODEV;
>  
>  	if (of_property_match_string(node, "riscv,isa-extensions", "i") < 0 ||
> -	    of_property_match_string(node, "riscv,isa-extensions", "m") < 0 ||
> -	    of_property_match_string(node, "riscv,isa-extensions", "a") < 0) {
> -		pr_warn("CPU with hartid=%lu does not support ima", *hart);
> +	    of_property_match_string(node, "riscv,isa-extensions", "m") < 0) {
> +		pr_warn("CPU with hartid=%lu does not support im", *hart);
>  		return -ENODEV;
>  	}
> -
> +#if !defined(__riscv_atomic) && !defined(__riscv_zaamo) && !defined(__riscv_zalrsc)
> +#error "Need AMO or LR/SC atomics"
> +#endif
> +	/*
> +	 * Require each atomic form this kernel emits. The single-letter
> +	 * "a" extension satisfies either check. A Zalrsc-only build defines
> +	 * __riscv_zalrsc and checks that extension only.
> +	 */
> +#if defined(__riscv_atomic) || defined(__riscv_zaamo)
> +	if (of_property_match_string(node, "riscv,isa-extensions", "a") < 0 &&
> +	    of_property_match_string(node, "riscv,isa-extensions", "zaamo") < 0) {
> +		pr_warn("CPU with hartid=%lu does not support AMO atomics", *hart);
> +		return -ENODEV;
> +	}
> +#endif
> +#if defined(__riscv_atomic) || defined(__riscv_zalrsc)
> +	if (of_property_match_string(node, "riscv,isa-extensions", "a") < 0 &&
> +	    of_property_match_string(node, "riscv,isa-extensions", "zalrsc") < 0) {
> +		pr_warn("CPU with hartid=%lu does not support LR/SC atomics", *hart);
> +		return -ENODEV;
> +	}
> +#endif
>  	return 0;
>  
>  old_interface:
> 
> -- 
> 2.43.0
> 
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