linux-kernel - Re: [PATCH v2] drm/i915: Explicitly cast divisor and use div

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Message-ID: <ZrOLlofTKS_xKWrC@ashyti-mobl2.lan>
Date: Wed, 7 Aug 2024 15:58:30 +0100
From: Andi Shyti <andi.shyti@...ux.intel.com>
To: "Cavitt, Jonathan" <jonathan.cavitt@...el.com>
Cc: Thorsten Blum <thorsten.blum@...lux.com>,
	"jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
	"joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
	"Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
	"tursulin@...ulin.net" <tursulin@...ulin.net>,
	"airlied@...il.com" <airlied@...il.com>,
	"daniel@...ll.ch" <daniel@...ll.ch>,
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/i915: Explicitly cast divisor and use div_u64()

Hi Thorsten,

> >  			/* This check is primarily to ensure that oa_period <=
> > -			 * UINT32_MAX (before passing to do_div which only
> > +			 * UINT32_MAX (before passing it to div_u64 which only
> >  			 * accepts a u32 denominator), but we can also skip
> >  			 * checking anything < 1Hz which implicitly can't be
> >  			 * limited via an integer oa_max_sample_rate.
> >  			 */
> >  			if (oa_period <= NSEC_PER_SEC) {
> > -				u64 tmp = NSEC_PER_SEC;
> > -				do_div(tmp, oa_period);
> > -				oa_freq_hz = tmp;
> > +				oa_freq_hz = div_u64(NSEC_PER_SEC, (u32)oa_period);
> >  			} else
> >  				oa_freq_hz = 0;
> 
> Non-blocking suggestion: this looks like it can be inlined.  And if the
> inline route is taken, it might be best to invert the conditional check
> like such:
> 
> oa_freq_hz = oa_period > NSEC_PER_SEC ? 0 :
>                                      div_u64(NSEC_PER_SEC, (u32)oa_period);
> 
> I think this is just a matter of preference, though.  The explicit if-else
> block is definitely clearer.

It's also stylistically wrong given that now the if/else don't
need the brackets anymore, triggering a checkpatch error.

Thorsten do you mind resending it either following Jonathan's
suggestion (my favourite, as well) or fix the bracket issue
following the kernel style.

Andi