Re: [PATCH 2/7] hwmon: (pmbus/adm1266) write fractional-seconds field of SET_RTC

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] 64-bit division using the `/` operator will cause build failures on 32-bit architectures.
--

commit f0fa424ad89f6e68ea279a8fd355cf480c9af8fc
Author: Abdurrahman Hussain <abdurrahman@nexthop.ai>

hwmon: (pmbus/adm1266) write fractional-seconds field of SET_RTC

This commit updates the adm1266 driver to write the fractional-seconds field
of the SET_RTC register. It samples wall-clock time as a struct timespec64
and converts tv_nsec to a 16-bit fractional representation using 64-bit
arithmetic.

> diff --git a/drivers/hwmon/pmbus/adm1266.c b/drivers/hwmon/pmbus/adm1266.c
> index a86666c73a5e9..ba8a025095287 100644
> --- a/drivers/hwmon/pmbus/adm1266.c
> +++ b/drivers/hwmon/pmbus/adm1266.c
[ ... ]
> @@ -428,16 +428,23 @@ static int adm1266_config_nvmem(struct adm1266_data *data)
[ ... ]
> +	/*
> +	 * SET_RTC frame layout (datasheet Rev. D, Table 84):
> +	 *   bytes [1:0] = fractional seconds, LSB = 1/65536 s
> +	 *   bytes [5:2] = seconds since 1970-01-01 UTC
> +	 */
> +	frac = (u16)(((u64)ts.tv_nsec << 16) / NSEC_PER_SEC);

Will this cause build failures on 32-bit architectures?

The compiler lacks built-in hardware support for 64-bit division on 32-bit
architectures and emits a call to an intrinsic like __udivdi3, which is not
available since the kernel does not link with libgcc.

Should this use the div_u64() helper function instead, such as
div_u64((u64)ts.tv_nsec << 16, NSEC_PER_SEC)?

> +	for (i = 0; i < 2; i++)
> +		write_buf[i] = (frac >> (i * 8)) & 0xFF;
>  	for (i = 0; i < 4; i++)
> -		write_buf[2 + i] = (kt >> (i * 8)) & 0xFF;
> +		write_buf[2 + i] = (ts.tv_sec >> (i * 8)) & 0xFF;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260508-adm1266-v1-0-ec08bf29e0ce@nexthop.ai?part=2