Re: [PATCH] ASoC: sophgo: fix 64-bit division build failure

[Alexander Sverdlin]

Hi Arnd!

On Mon, 2026-02-02 at 10:53 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> cv1800b_adc_setbclk_div() does four 64-bit divisions in a row, which

3 of the 4 divisors are actually a power of two, so it would be a bug
in the compiler to issue a division for them...

Regarding the 64 bits: seems that the actual issue is the tmp variable that
is of u64 type for no reason, because priv->mclk_rate is only u32.

Maybe turning tmp into a u32 would avoid unnecessary 64-bit division
altogether?

> is rather inefficient on 32-bit systems, and using the plain division
> causes a build failure as a result:
> 
> ERROR: modpost: "__aeabi_uldivmod" [sound/soc/sophgo/cv1800b-sound-adc.ko] undefined!
> 
> Consolidate those into a single division using the div_u64() macro.
> 
> Fixes: 4cf8752a03e6 ("ASoC: sophgo: add CV1800B internal ADC codec driver")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  sound/soc/sophgo/cv1800b-sound-adc.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/sound/soc/sophgo/cv1800b-sound-adc.c b/sound/soc/sophgo/cv1800b-sound-adc.c
> index 794030b713e9..b66761156b99 100644
> --- a/sound/soc/sophgo/cv1800b-sound-adc.c
> +++ b/sound/soc/sophgo/cv1800b-sound-adc.c
> @@ -105,11 +105,8 @@ static int cv1800b_adc_setbclk_div(struct cv1800b_priv *priv, unsigned int rate)
>  	if (!priv->mclk_rate || !rate)
>  		return -EINVAL;
>  
> -	tmp = priv->mclk_rate;
> -	tmp /= CV1800B_RXADC_WORD_LEN;
> -	tmp /= CV1800B_RXADC_CHANNELS;
> -	tmp /= rate;
> -	tmp /= 2;
> +	tmp = div_u64(priv->mclk_rate, CV1800B_RXADC_WORD_LEN *
> +		      CV1800B_RXADC_CHANNELS * rate * 2);
>  
>  	if (!tmp) {
>  		dev_err(priv->dev, "computed BCLK divider is zero\n");

-- 
Alexander Sverdlin.