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clocksource: Provide a generic mult/shift factor calculation

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MIPS has two functions to calculcate the mult/shift factors for clock
sources and clock events at run time. ARM needs such functions as
well.

Implement a function which calculates the mult/shift factors based on
the frequencies to which and from which is converted. The function
also has a parameter to specify the minimum conversion range in
seconds. This range is guaranteed not to produce a 64bit overflow when
a value is multiplied with the calculated mult factor. The larger the
conversion range the less becomes the conversion accuracy.

Provide two inline wrappers which handle clock events and clock
sources. For clock events the "from" frequency is nano seconds per
second which corresponds to 1GHz and "to" is the device frequency. For
clock sources "from" is the device frequency and "to" is nano seconds
per second.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mikael Pettersson <mikpe@it.uu.se>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Cc: John Stultz <johnstul@us.ibm.com>
LKML-Reference: <20091111134229.766673305@linutronix.de>
This commit is contained in:
Thomas Gleixner 2009-11-11 14:05:29 +00:00
parent 23af368e9a
commit 7d2f944a2b
3 changed files with 70 additions and 0 deletions
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7
include/linux/clockchips.h
View file

@ -130,6 +130,13 @@ extern int clockevents_program_event(struct clock_event_device *dev,
extern void clockevents_handle_noop(struct clock_event_device *dev);
static inline void
clockevents_calc_mult_shift(struct clock_event_device *ce, u32 freq, u32 minsec)
{
return clocks_calc_mult_shift(&ce->mult, &ce->shift, NSEC_PER_SEC,
freq, minsec);
}
#ifdef CONFIG_GENERIC_CLOCKEVENTS
extern void clockevents_notify(unsigned long reason, void *arg);
#else