Re: [PATCH] ASoC: tegra: tegra210-mixer: Use div_u64() for 64-bit division

[Nathan Chancellor <nathan@kernel.org>]

On Thu, May 07, 2026 at 04:21:31PM -0700, Rosen Penev wrote:
> A MIPS allmodconfig build with LLVM fails during modpost:
> 
>   ERROR: modpost: "__udivdi3"
>   [sound/soc/tegra/snd-soc-tegra210-mixer.ko] undefined!
> 
> tegra210_mixer_configure_gain() divides a 64-bit BIT_ULL() value by the
> fade duration. On 32-bit MIPS, clang emits a call to __udivdi3 for that
> plain C division, but that compiler helper is not exported to modules.
> 
> Use div_u64() for the inverse duration calculation so the driver uses the
> kernel's 64-bit division helper instead of emitting a compiler runtime
> call.
> 
> Assisted-by: Codex:GPT-5.5
> Signed-off-by: Rosen Penev <rosenp@gmail.com>

This is neither a Clang nor MIPS specific issue, it will happen with any
32-bit target, as Arnd's patch shows:

  https://lore.kernel.org/20260508080031.4064272-1-arnd@kernel.org/

Regardless, this is obviously the correct fix.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  sound/soc/tegra/tegra210_mixer.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/soc/tegra/tegra210_mixer.c b/sound/soc/tegra/tegra210_mixer.c
> index f05617b5f433..bfdd457f740c 100644
> --- a/sound/soc/tegra/tegra210_mixer.c
> +++ b/sound/soc/tegra/tegra210_mixer.c
> @@ -7,6 +7,7 @@
>  #include <linux/clk.h>
>  #include <linux/device.h>
>  #include <linux/io.h>
> +#include <linux/math64.h>
>  #include <linux/mod_devicetable.h>
>  #include <linux/module.h>
>  #include <linux/platform_device.h>
> @@ -157,8 +158,8 @@ static int tegra210_mixer_configure_gain(struct snd_soc_component *cmpnt,
>  			if (i == DURATION_N3_ID)
>  				val = mixer->duration[id];
>  			else if (i == DURATION_INV_N3_ID)
> -				val = (u32)(BIT_ULL(31 + TEGRA210_MIXER_PRESCALAR) /
> -					    mixer->duration[id]);
> +				val = div_u64(BIT_ULL(31 + TEGRA210_MIXER_PRESCALAR),
> +					      mixer->duration[id]);
>  			else
>  				val = gain_params.duration[i];
>  		}
> -- 
> 2.54.0
> 

-- 
Cheers,
Nathan