linux-kernel - Re: [RFC PATCH v4 04/21] x86/hpet: Add hpet_set_comparator() for periodic and one-shot modes

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Message-ID: <20190618224835.GF30488@ranerica-svr.sc.intel.com>
Date:   Tue, 18 Jun 2019 15:48:35 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Ashok Raj <ashok.raj@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <andi.kleen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Stephane Eranian <eranian@...gle.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Ricardo Neri <ricardo.neri@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH v4 04/21] x86/hpet: Add hpet_set_comparator() for
 periodic and one-shot modes

On Fri, Jun 14, 2019 at 08:17:14PM +0200, Thomas Gleixner wrote:
> On Thu, 23 May 2019, Ricardo Neri wrote:
> > +/**
> > + * hpet_set_comparator() - Helper function for setting comparator register
> > + * @num:	The timer ID
> > + * @cmp:	The value to be written to the comparator/accumulator
> > + * @period:	The value to be written to the period (0 = oneshot mode)
> > + *
> > + * Helper function for updating comparator, accumulator and period values.
> > + *
> > + * In periodic mode, HPET needs HPET_TN_SETVAL to be set before writing
> > + * to the Tn_CMP to update the accumulator. Then, HPET needs a second
> > + * write (with HPET_TN_SETVAL cleared) to Tn_CMP to set the period.
> > + * The HPET_TN_SETVAL bit is automatically cleared after the first write.
> > + *
> > + * For one-shot mode, HPET_TN_SETVAL does not need to be set.
> > + *
> > + * See the following documents:
> > + *   - Intel IA-PC HPET (High Precision Event Timers) Specification
> > + *   - AMD-8111 HyperTransport I/O Hub Data Sheet, Publication # 24674
> > + */
> > +void hpet_set_comparator(int num, unsigned int cmp, unsigned int period)
> > +{
> > +	if (period) {
> > +		unsigned int v = hpet_readl(HPET_Tn_CFG(num));
> > +
> > +		hpet_writel(v | HPET_TN_SETVAL, HPET_Tn_CFG(num));
> > +	}
> > +
> > +	hpet_writel(cmp, HPET_Tn_CMP(num));
> > +
> > +	if (!period)
> > +		return;
> 
> TBH, I hate this conditional handling. What's wrong with two functions?

There is probably nothing wrong with two functions. I can split it into
hpet_set_comparator_periodic() and hpet_set_comparator(). Perhaps the
latter is not needed as it would be a one-line function; you have
suggested earlier to avoid such small functions.
> 
> > +
> > +	/*
> > +	 * This delay is seldom used: never in one-shot mode and in periodic
> > +	 * only when reprogramming the timer.
> > +	 */
> > +	udelay(1);
> > +	hpet_writel(period, HPET_Tn_CMP(num));
> > +}
> > +EXPORT_SYMBOL_GPL(hpet_set_comparator);
> 
> Why is this exported? Which module user needs this?

It is not used anywhere else. I will remove this export.

Thanks and BR,

Ricardo