linux-kernel - Re: [RFC PATCH v3 04/21] x86/hpet: Add hpet_set_comparator() for periodic and one-shot modes

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Date:   Wed, 15 May 2019 08:56:04 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>, 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>,
        Stephane Eranian <eranian@...gle.com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Subject: Re: [RFC PATCH v3 04/21] x86/hpet: Add hpet_set_comparator() for
 periodic and one-shot modes

On Tue, May 14, 2019 at 07:24:38AM -0700, Randy Dunlap wrote:
> On 5/14/19 7:01 AM, Ricardo Neri wrote:
> > Instead of setting the timer period directly in hpet_set_periodic(), add a
> > new helper function hpet_set_comparator() that only sets the accumulator
> > and comparator. hpet_set_periodic() will only prepare the timer for
> > periodic mode and leave the expiration programming to
> > hpet_set_comparator().
> > 
> > This new function can also be used by other components (e.g., the HPET-
> > based hardlockup detector) which also need to configure HPET timers. Thus,
> > add its declaration into the hpet header file.
> > 
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Cc: Ashok Raj <ashok.raj@...el.com>
> > Cc: Andi Kleen <andi.kleen@...el.com>
> > Cc: Tony Luck <tony.luck@...el.com>
> > Cc: Philippe Ombredanne <pombredanne@...b.com>
> > Cc: Kate Stewart <kstewart@...uxfoundation.org>
> > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
> > Cc: Stephane Eranian <eranian@...gle.com>
> > Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> > Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
> > Cc: x86@...nel.org
> > Originally-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> > ---
> >  arch/x86/include/asm/hpet.h |  1 +
> >  arch/x86/kernel/hpet.c      | 57 ++++++++++++++++++++++++++++---------
> >  2 files changed, 45 insertions(+), 13 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h
> > index f132fbf984d4..e7098740f5ee 100644
> > --- a/arch/x86/include/asm/hpet.h
> > +++ b/arch/x86/include/asm/hpet.h
> > @@ -102,6 +102,7 @@ extern int hpet_rtc_timer_init(void);
> >  extern irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id);
> >  extern int hpet_register_irq_handler(rtc_irq_handler handler);
> >  extern void hpet_unregister_irq_handler(rtc_irq_handler handler);
> > +extern void hpet_set_comparator(int num, unsigned int cmp, unsigned int period);
> >  
> >  #endif /* CONFIG_HPET_EMULATE_RTC */
> >  
> > diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> > index 560fc28e1d13..c5c5fc150193 100644
> > --- a/arch/x86/kernel/hpet.c
> > +++ b/arch/x86/kernel/hpet.c
> > @@ -289,6 +289,46 @@ static void hpet_legacy_clockevent_register(void)
> >  	printk(KERN_DEBUG "hpet clockevent registered\n");
> >  }
> >  
> > +/**
> > + * 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;
> > +
> > +	/* This delay is seldom used: never in one-shot mode and in periodic
> > +	 * only when reprogramming the timer.
> > +	 */
> 
> comment style warning ;)
>

Uh! I'll correct this. Strangely, I reran checkpatch and it didn't catch
it.

Thanks and BR,
Ricardo