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Date: Wed, 15 May 2019 08:54:26 -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>, Clemens Ladisch <clemens@...isch.de>, Arnd Bergmann <arnd@...db.de>, 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 03/21] x86/hpet: Calculate ticks-per-second in a separate function On Tue, May 14, 2019 at 07:23:47AM -0700, Randy Dunlap wrote: > On 5/14/19 7:01 AM, Ricardo Neri wrote: > > It is easier to compute the expiration times of an HPET timer by using > > its frequency (i.e., the number of times it ticks in a second) than its > > period, as given in the capabilities register. > > > > In addition to the HPET char driver, the HPET-based hardlockup detector > > will also need to know the timer's frequency. Thus, create a common > > function that both can use. > > > > 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: Clemens Ladisch <clemens@...isch.de> > > Cc: Arnd Bergmann <arnd@...db.de> > > 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 > > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> > > --- > > drivers/char/hpet.c | 31 ++++++++++++++++++++++++------- > > include/linux/hpet.h | 1 + > > 2 files changed, 25 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c > > index d0ad85900b79..bdcbecfdb858 100644 > > --- a/drivers/char/hpet.c > > +++ b/drivers/char/hpet.c > > @@ -836,6 +836,29 @@ static unsigned long hpet_calibrate(struct hpets *hpetp) > > return ret; > > } > > > > +u64 hpet_get_ticks_per_sec(u64 hpet_caps) > > +{ > > + u64 ticks_per_sec, period; > > + > > + period = (hpet_caps & HPET_COUNTER_CLK_PERIOD_MASK) >> > > + HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */ > > + > > + /* > > + * The frequency is the reciprocal of the period. The period is given > > + * femtoseconds per second. Thus, prepare a dividend to obtain the > > * in femtoseconds per second. > Thanks for your review Randy! I'll fix this grammar issue. > > + * frequency in ticks per second. > > + */ > > + > > + /* 10^15 femtoseconds per second */ > > + ticks_per_sec = 1000000000000000uLL; > > ULL is overwhelmingly used in the kernel. > Sure, I'll update it. BR, Ricardo
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