[U-Boot] [PATCH 4/4] ARM: bcm283x: Switch to generic timer

Stephen Warren
2015-05-05T22:37:38Z

On 05/05/2015 04:17 PM, Marek Vasut wrote:
> 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 ?

Sorry, I still don't understand. Both the __udelay() here and in
lib/time.c take an unsigned long argument. I don't see how switching one
out for the other can affect anything if the argument type is the issue.
Besides, what's passing a value >~36 minutes to udelay()?