Re: [RFC PATCH v2 03/14] x86/hpet: Calculate ticks-per-second in a separate function
On Tue, Mar 26, 2019 at 10:03:02PM +0100, Thomas Gleixner wrote:
> On Wed, 27 Feb 2019, Ricardo Neri wrote:
> > int hpet_alloc(struct hpet_data *hdp)
> > {
> > u64 cap, mcfg;
> > @@ -845,7 +868,6 @@ int hpet_alloc(struct hpet_data *hdp)
> > size_t siz;
> > struct hpet __iomem *hpet;
> > static struct hpets *last;
> > - unsigned long period;
> > unsigned long long temp;
> > u32 remainder;
> >
> > @@ -881,6 +903,8 @@ int hpet_alloc(struct hpet_data *hdp)
> >
> > cap = readq(>hpet_cap);
> >
> > + temp = hpet_get_ticks_per_sec(cap);
>
> Just putting stuff to random places does not make the code any better.
This seems to not be needed. I'll remove it and directly save the result
in hpetp->hp_tick_freq;
>
> > ntimer = ((cap & HPET_NUM_TIM_CAP_MASK) >> HPET_NUM_TIM_CAP_SHIFT) + 1;
> >
> > if (hpetp->hp_ntimer != ntimer) {
> > @@ -897,11 +921,6 @@ 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 = 1000uLL; /* 10^15 femtoseconds per second */
> > - temp += period >> 1; /* round */
> > - do_div(temp, period);
> > hpetp->hp_tick_freq = temp; /* ticks per second */
>
> What's wrong with the obvious:
>
>hpetp->hp_tick_freq = hpet_get_ticks_per_sec(cap);
>
> Hmm?
Nothing wrong. I'll implement this change.
Thanks and BR,
Ricardo
Re: [RFC PATCH v2 03/14] x86/hpet: Calculate ticks-per-second in a separate function
On Wed, 27 Feb 2019, Ricardo Neri wrote:
> int hpet_alloc(struct hpet_data *hdp)
> {
> u64 cap, mcfg;
> @@ -845,7 +868,6 @@ int hpet_alloc(struct hpet_data *hdp)
> size_t siz;
> struct hpet __iomem *hpet;
> static struct hpets *last;
> - unsigned long period;
> unsigned long long temp;
> u32 remainder;
>
> @@ -881,6 +903,8 @@ int hpet_alloc(struct hpet_data *hdp)
>
> cap = readq(>hpet_cap);
>
> + temp = hpet_get_ticks_per_sec(cap);
Just putting stuff to random places does not make the code any better.
> ntimer = ((cap & HPET_NUM_TIM_CAP_MASK) >> HPET_NUM_TIM_CAP_SHIFT) + 1;
>
> if (hpetp->hp_ntimer != ntimer) {
> @@ -897,11 +921,6 @@ 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 = 1000uLL; /* 10^15 femtoseconds per second */
> - temp += period >> 1; /* round */
> - do_div(temp, period);
> hpetp->hp_tick_freq = temp; /* ticks per second */
What's wrong with the obvious:
hpetp->hp_tick_freq = hpet_get_ticks_per_sec(cap);
Hmm?
Thanks,
tglx
[RFC PATCH v2 03/14] x86/hpet: Calculate ticks-per-second in a separate function
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"
Cc: Ashok Raj
Cc: Andi Kleen
Cc: Tony Luck
Cc: Clemens Ladisch
Cc: Arnd Bergmann
Cc: Philippe Ombredanne
Cc: Kate Stewart
Cc: "Rafael J. Wysocki"
Cc: "Ravi V. Shankar"
Cc: x...@kernel.org
Signed-off-by: Ricardo Neri
---
drivers/char/hpet.c | 31 +--
include/linux/hpet.h | 1 +
2 files changed, 26 insertions(+), 6 deletions(-)
diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 4a22b4b41aef..b73b68c0e127 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
+* frequency in ticks per second.
+*/
+
+ /* 10^15 femtoseconds per second */
+ ticks_per_sec = 1000uLL;
+ 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;
@@ -845,7 +868,6 @@ int hpet_alloc(struct hpet_data *hdp)
size_t siz;
struct hpet __iomem *hpet;
static struct hpets *last;
- unsigned long period;
unsigned long long temp;
u32 remainder;
@@ -881,6 +903,8 @@ int hpet_alloc(struct hpet_data *hdp)
cap = readq(>hpet_cap);
+ temp = hpet_get_ticks_per_sec(cap);
+
ntimer = ((cap & HPET_NUM_TIM_CAP_MASK) >> HPET_NUM_TIM_CAP_SHIFT) + 1;
if (hpetp->hp_ntimer != ntimer) {
@@ -897,11 +921,6 @@ 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 = 1000uLL; /* 10^15 femtoseconds per second */
- temp += period >> 1; /* round */
- do_div(temp, period);
hpetp->hp_tick_freq = temp; /* ticks per second */
printk(KERN_INFO "hpet%d: at MMIO 0x%lx, IRQ%s",
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__ */
--
2.17.1
