On Tuesday, May 05, 2015 at 11:46:56 PM, Stephen Warren wrote:
> On 05/04/2015 02:54 PM, Marek Vasut wrote:
> > Switch to generic timer implementation from lib/time.c .
> > This also fixes a signed overflow which was in __udelay()
> > implementation.
>
> Can you explain that a bit more?
>
> > -void __udelay(unsigned long usec)
> > -{
> > - ulong endtime;
> > - signed long diff;
> > -
> > - endtime = get_timer_us(0) + usec;
> > -
> > - do {
> > - ulong now = get_timer_us(0);
> > - diff = endtime - now;
> > - } while (diff >= 0);
> > -}
>
> I believe since endtime and now hold micro seconds, there shouldn't be
> any overflow so long as the microsecond difference fits into 31 bits,
> i.e. so long as usec is less than ~36 minutes. I doubt anything is
> calling __udelay() with that large of a value. Perhaps the issue this
> patch fixes is in get_timer_us(0) instead, or something else changed as
> a side-effect?
The generic implementation caters for full 32-bit range, that's all.
Since the argument of this function is unsigned, it can overflow if
you use argument which is bigger than 31 bits. OK like that ?
Best regards,
Marek Vasut
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