linux-kernel - Re: [PATCH] drm/i915: Explicitly cast divisor to fix Coccinelle warning

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Message-ID: <Zo5yvk69FB-jEgd8@intel.com>
Date: Wed, 10 Jul 2024 14:38:38 +0300
From: Ville Syrjälä <ville.syrjala@...ux.intel.com>
To: Thorsten Blum <thorsten.blum@...lux.com>
Cc: jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
	rodrigo.vivi@...el.com, tursulin@...ulin.net, airlied@...il.com,
	daniel@...ll.ch, intel-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915: Explicitly cast divisor to fix Coccinelle
 warning

On Wed, Jul 10, 2024 at 09:46:51AM +0200, Thorsten Blum wrote:
> As the comment explains, the if check ensures that the divisor oa_period
> is a u32. Explicitly cast oa_period to u32 to remove the following
> Coccinelle/coccicheck warning reported by do_div.cocci:
> 
>   WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>
> ---
>  drivers/gpu/drm/i915/i915_perf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index 0b1cd4c7a525..24722e758aaf 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -4103,7 +4103,7 @@ static int read_properties_unlocked(struct i915_perf *perf,
>  			 */
>  			if (oa_period <= NSEC_PER_SEC) {
>  				u64 tmp = NSEC_PER_SEC;
> -				do_div(tmp, oa_period);
> +				do_div(tmp, (u32)oa_period);

Why is this code even using do_div() when it doesn't need the
remainder?

>  				oa_freq_hz = tmp;
>  			} else
>  				oa_freq_hz = 0;
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel