[PATCH v3 1/4] timer: Allow delays with a 32-bit microsecond timer

Simon Glass sjg at chromium.org
Mon Jul 13 04:25:10 CEST 2020


Hi Bin,

On Sun, 12 Jul 2020 at 20:13, Bin Meng <bmeng.cn at gmail.com> wrote:
>
> On Fri, Jul 10, 2020 at 8:49 AM Simon Glass <sjg at chromium.org> wrote:
> >
> > The current get_timer_us() uses 64-bit arithmetic on 32-bit machines.
> > When implementing microsecond-level timeouts, 32-bits is plenty. Add a
> > new function that uses an unsigned long. On 64-bit machines this is
> > still 64-bit, but this doesn't introduce a penalty. On 32-bit machines
> > it is more efficient.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > ---
> >
> > Changes in v3:
> > - Expand the commit message and function comment
> >
> >  include/time.h | 11 +++++++++++
> >  lib/time.c     |  5 +++++
> >  2 files changed, 16 insertions(+)
> >
> > diff --git a/include/time.h b/include/time.h
> > index e99f9c8012..3f00e68713 100644
> > --- a/include/time.h
> > +++ b/include/time.h
> > @@ -17,6 +17,17 @@ unsigned long get_timer(unsigned long base);
> >  unsigned long timer_get_us(void);
> >  uint64_t get_timer_us(uint64_t base);
> >
> > +/**
> > + * get_timer_us_long() - Get the number of elapsed microseconds
> > + *
> > + * This uses 32-bit arithmetic on 32-bit machines, which is enough to handle
> > + * delays of over an hour. For 64-bit machines it uses a 64-bit value.
> > + *
> > + *@base: Base time to consider
> > + *@return elapsed time since @base
> > + */
> > +unsigned long get_timer_us_long(unsigned long base);
> > +
> >  /*
> >   * timer_test_add_offset()
> >   *
> > diff --git a/lib/time.c b/lib/time.c
> > index 65db0f6cda..47f8c84327 100644
> > --- a/lib/time.c
> > +++ b/lib/time.c
> > @@ -152,6 +152,11 @@ uint64_t __weak get_timer_us(uint64_t base)
> >         return tick_to_time_us(get_ticks()) - base;
> >  }
> >
> > +unsigned long __weak get_timer_us_long(unsigned long base)
> > +{
> > +       return timer_get_us() - base;
> > +}
> > +
> >  unsigned long __weak notrace timer_get_us(void)
> >  {
> >         return tick_to_time(get_ticks() * 1000);
> > --
>
> Reviewed-by: Bin Meng <bmeng.cn at gmail.com>
>
> Some day we should clean up the timer APIs. We have get_timer_us(),
> and now get_timer_us_long(), but we also have timer_get_us() that
> returns long value!

Yes, but that one returns the monotonic time, so isn't so easy for
timeouts. Perhaps we should remove it since get_timer_us_long(0) does
the same thing?

Regards,
Simon


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