Messages in this thread |  | | Subject | Re: [RFC PATCH v3 03/21] x86/hpet: Calculate ticks-per-second in a separate function | From | Randy Dunlap <> | Date | Tue, 14 May 2019 07:23:47 -0700 |
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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@zytor.com> > Cc: Ashok Raj <ashok.raj@intel.com> > Cc: Andi Kleen <andi.kleen@intel.com> > Cc: Tony Luck <tony.luck@intel.com> > Cc: Clemens Ladisch <clemens@ladisch.de> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Philippe Ombredanne <pombredanne@nexb.com> > Cc: Kate Stewart <kstewart@linuxfoundation.org> > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> > Cc: Stephane Eranian <eranian@google.com> > Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> > Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com> > Cc: x86@kernel.org > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.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.
> + * frequency in ticks per second. > + */ > + > + /* 10^15 femtoseconds per second */ > + ticks_per_sec = 1000000000000000uLL;
ULL is overwhelmingly used in the kernel.
> + ticks_per_sec += period >> 1; /* round */ > + > + /* The quotient is put in the dividend. We drop the remainder. */ > + do_div(ticks_per_sec, period); > + > + return ticks_per_sec; > +} > + > int hpet_alloc(struct hpet_data *hdp) > { > u64 cap, mcfg; > @@ -844,7 +867,6 @@ int hpet_alloc(struct hpet_data *hdp) > struct hpets *hpetp; > struct hpet __iomem *hpet; > static struct hpets *last; > - unsigned long period; > unsigned long long temp; > u32 remainder; > > @@ -894,12 +916,7 @@ int hpet_alloc(struct hpet_data *hdp) > > last = hpetp; > > - period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >> > - HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */ > - temp = 1000000000000000uLL; /* 10^15 femtoseconds per second */ > - temp += period >> 1; /* round */ > - do_div(temp, period); > - hpetp->hp_tick_freq = temp; /* ticks per second */ > + hpetp->hp_tick_freq = hpet_get_ticks_per_sec(cap); > > printk(KERN_INFO "hpet%d: at MMIO 0x%lx, IRQ%s", > hpetp->hp_which, hdp->hd_phys_address, > diff --git a/include/linux/hpet.h b/include/linux/hpet.h > index 8604564b985d..e7b36bcf4699 100644 > --- a/include/linux/hpet.h > +++ b/include/linux/hpet.h > @@ -107,5 +107,6 @@ static inline void hpet_reserve_timer(struct hpet_data *hd, int timer) > } > > int hpet_alloc(struct hpet_data *); > +u64 hpet_get_ticks_per_sec(u64 hpet_caps); > > #endif /* !__HPET__ */ >
-- ~Randy
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