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

[Bin Meng]

Hi Simon,

On Mon, Jul 13, 2020 at 10:25 AM Simon Glass <sjg at chromium.org> wrote:
>
> 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?

Yes, I think so.

Regards,
Bin