lkml.org 
[lkml]   [2019]   [May]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC PATCH v3 03/21] x86/hpet: Calculate ticks-per-second in a separate function
From
Date
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

\
 
 \ /
  Last update: 2019-05-14 16:25    [W:0.095 / U:4.860 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site