linux-kernel - Re: [PATCH] Make MIPS dynamic clocksource/clockevent clock code generic

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Message-ID: <19165.29312.300540.500942@pilspetsen.it.uu.se>
Date:	Tue, 20 Oct 2009 10:19:12 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-mips@...ux-mips.org, Ralf Baechle <ralf@...ux-mips.org>,
	Mikael Pettersson <mikpe@...uu.se>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] Make MIPS dynamic clocksource/clockevent clock code
	generic

Thomas Gleixner writes:
 > > +static inline void clockevent_set_clock(struct clock_event_device *dev, u32 hz)
 > > +{
 > > +	u64 temp;
 > > +	u32 shift;
 > > +
 > > +	/* Find a shift value */
 > > +	for (shift = 32; shift > 0; shift--) {
 > > +		temp = (u64) hz << shift;
 > > +		do_div(temp, NSEC_PER_SEC);
 > > +		if ((temp >> 32) == 0)
 > > +			break;
 > > +	}
 > > +	dev->shift = shift;
 > > +	dev->mult = (u32) temp;
 > > +}
 > > +
 > > +
 > > +static inline void clocksource_set_clock(struct clocksource *cs, u32 hz)
 > > +{
 > > +	u64 temp;
 > > +	u32 shift;
 > > +
 > > +	/* Find a shift value */
 > > +	for (shift = 32; shift > 0; shift--) {
 > > +		temp = (u64) NSEC_PER_SEC << shift;
 > > +		do_div(temp, hz);
 > > +		if ((temp >> 32) == 0)
 > > +			break;
 > > +	}
 > > +	cs->shift = shift;
 > > +	cs->mult = (u32) temp;
 > > +}
 > > +
 > 
 > So that's the same function twice, right ?

They are similar but not identical:

 > > +		temp = (u64) hz << shift;
 > > +		do_div(temp, NSEC_PER_SEC);

vs

 > > +		temp = (u64) NSEC_PER_SEC << shift;
 > > +		do_div(temp, hz);

I suppose both functions could be implemented by a suitably
parametric third function, but IMO that would just obscure things.

Making them non-inline I fully agree with.
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