linux-kernel - Re: [PATCH] math64: Provide an uprounding variant of mul_u64_u64_div

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Message-ID: <66rr3q6p-2449-6722-0716-s5245pq4on9r@onlyvoer.pbz>
Date: Wed, 19 Mar 2025 15:38:03 -0400 (EDT)
From: Nicolas Pitre <npitre@...libre.com>
To: Uwe Kleine-König <u.kleine-koenig@...libre.com>
cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] math64: Provide an uprounding variant of
 mul_u64_u64_div_u64()

On Wed, 19 Mar 2025, Uwe Kleine-König wrote:

> This is needed (at least) in the pwm-stm32 driver. Currently the
> pwm-stm32 driver implements this function itself. This private
> implementation can be dropped as a followup of this patch.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...libre.com>
> ---
[...]
> +#ifndef mul_u64_u64_div_u64_roundup
> +u64 mul_u64_u64_div_u64_roundup(u64 a, u64 b, u64 c)
> +{
> +	u64 res = mul_u64_u64_div_u64(a, b, c);
> +	/* Those multiplications might overflow but it doesn't matter */
> +	u64 rem = a * b - c * res;
> +
> +	if (rem)
> +		res += 1;
> +
> +	return res;
> +}
> +EXPORT_SYMBOL(mul_u64_u64_div_u64_roundup);
> +#endif

Might there ever be a need for a _rem variant similar to 
div64_u64_rem()? If so the _roundup could then be a simple wrapper.

Otherwise:

Reviewed-by: Nicolas Pitre <npitre@...libre.com>