[PATCH 1/2] clk: imx: do not sleep if IRQ's are still disabled

Stefan Agner
2016-04-27T07:28:10Z

On 2016-04-26 19:56, Fabio Estevam wrote:
> On Tue, Apr 26, 2016 at 11:45 PM, Dong Aisheng <dongas86@gmail.com> wrote:
>
>>> We need to firstly understand why this is happening. The .prepare hook
>>> is defined to be non-atomic context, and so that we call sleep function
>>> in there. We did everything right. Why are we getting the warning? If
>>> I'm correct, this warning only happens on i.MX7D. Why is that?
>>>
>>
>> This is mainly caused by during kernel early booting, there's only one init idle
>> task running.
>> See:
>> void __init sched_init(void)
>> {
>> .....
>> /*
>> * Make us the idle thread. Technically, schedule() should not be
>> * called from this thread, however somewhere below it might be,
>> * but because we are the idle thread, we just pick up running again
>> * when this runqueue becomes "idle".
>> */
>> init_idle(current, smp_processor_id());
>> ...
>> }
>>
>> And the idle sched class indicates it's not valid to schedule for idle task.
>> const struct sched_class idle_sched_class = {
>> /* .next is NULL */
>> /* no enqueue/yield_task for idle tasks */
>>
>> /* dequeue is not valid, we print a debug message there: */
>> .dequeue_task = dequeue_task_idle,
>> ...........
>>
>> }
>>
>> /*
>> * It is not legal to sleep in the idle task - print a warning
>> * message if some code attempts to do it:
>> */
>> static void
>> dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
>> {
>> raw_spin_unlock_irq(&rq->lock);
>> printk(KERN_ERR "bad: scheduling from the idle thread!\n");
>> dump_stack();
>> raw_spin_lock_irq(&rq->lock);
>> }
>>
>>
>> Below is the full log of imx7d booting FYI.
>
> This does not answer Shawn's question: why do we see this only on mx7d?

I was wondering that too.... My theory is that either on i.MX 6 the
clocks enable almost instantly leading to no sleep, or they are just
bootloader/firmware on...?

--
Stefan