Re: [PATCH v16 03/16] arm64/delay: move, fixup usecs_to_cycles()

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, Oct 16, 2026 at 12:08:24AM -0700, Ankur Arora wrote:
> diff --git a/arch/arm64/include/asm/delay-const.h b/arch/arm64/include/asm/delay-const.h
> new file mode 100644
> index 000000000000..6ccdfe0a4130
> --- /dev/null
> +++ b/arch/arm64/include/asm/delay-const.h
> @@ -0,0 +1,35 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef _ASM_DELAY_CONST_H
> +#define _ASM_DELAY_CONST_H
> +
> +#include <linux/math64.h>
> +#include <linux/types.h>
> +#include <asm/param.h>	/* For HZ */
> +
> +/* 2**32 / 1000000 (rounded up) */
> +#define __usecs_to_xloops_mult	0x10C7UL
> +
> +/* 2**32 / 1000000000 (rounded up) */
> +#define __nsecs_to_xloops_mult	0x5UL
> +
> +extern unsigned long loops_per_jiffy;
> +static inline u64 xloops_to_cycles(u64 xloops)
> +{
> +	u64 loops_per_sec = (u64)loops_per_jiffy * HZ;
> +
> +	return mul_u64_u64_shr(xloops, loops_per_sec, 32);
> +}
> +
> +static inline u64 usecs_to_cycles(u64 time_usecs)
> +{
> +	return xloops_to_cycles(time_usecs * __usecs_to_xloops_mult);
> +}
> +
> +static inline u64 nsecs_to_cycles(u64 time_nsecs)
> +{
> +	return xloops_to_cycles((time_nsecs) * __nsecs_to_xloops_mult);
> +}
> +
> +u64 notrace __delay_cycles(void);
> +
> +#endif	/* _ASM_DELAY_CONST_H */

The bot reports are valid, moving these into headers pulled elsewhere
will clash with existing functions with the same name. You fixed one but
there's another. Isn't it easier to just add an arm64_ prefix to these?

Alternatively, I think we only need nsecs_to_cycles(). We have an out of
line call to __delay_cycles() already, so can we not just add a new
function to use directly and avoid polluting the headers:

u64 arm64_wfet_deadline(u64 timeout_ns)
{
        return __delay_cycles() + nsecs_to_cycles(timeout_ns);
}
EXPORT_SYMBOL_GPL(arm64_wfet_deadline);

I prefer the latter if it works.

-- 
Catalin