Re: Regression on colibri-imx7 due to commit 9c1b13b3fd27 ("cyclic: reduce get_timer_us() calls inside hlist_for_each_entry_safe()")

[Emanuele Ghidoli <ghidoliemanuele@gmail.com>]

On 7/23/26 20:35, Marek Vasut wrote:
> On 7/23/26 4:53 PM, Emanuele Ghidoli wrote:
> 
> Hello everyone,
> 
>> I found that Colibri iMX7 no longer boots when commit 9c1b13b3fd27
>> ("cyclic: reduce get_timer_us() calls inside hlist_for_each_entry_safe()")
>> is applied. Nothing is printed on the serial.
>>
>> I bisected the issue: booting the parent commit works fine, and
>> reverting this patch on top of current main also restores
>> boot. It's not yet obvious to me what in this change causes the
>> regression.
>>
>> Would it make sense to revert it until the root cause is found?
> 
> Give Patrice a bit of time to analyze the problem.
> 

Hello,

after the regression, get_timer_us() is called on every cyclic_run() call,
even when the cyclic list is empty. On imx7 this happens earlier than before,
when the timer has not yet been initialized: get_timer_us() calls get_tbclk(),
whose value is zero, and uses it as a divisor in tick_to_time_us(), leading to
a division by zero.

I would fix this by ensuring get_tbclk() returns at least 1 on imx7, but we
could hide bugs in this way. However, this bug could also be present on other
architectures, so I would just guard against entering the cyclic loop by
checking whether the list is empty before doing anything else, so
get_timer_us() is called "at the same point in time" as before.
Something like:
if (hlist_empty(cyclic_get_list())) {
	gd->flags &= ~GD_FLG_CYCLIC_RUNNING;
	return;
}

Kind regards,
Emanuele