linux-kernel - Re: [PATCH 4.4-rt2] fix arm-at91-pit-remove-irq-handler-when-clock-is-unused.patch

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Date:	Mon, 18 Jan 2016 21:24:28 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: [PATCH 4.4-rt2] fix
 arm-at91-pit-remove-irq-handler-when-clock-is-unused.patch

On 01/18/2016 07:42 PM, Alexandre Belloni wrote:
> On 18/01/2016 at 18:25:22 +0100, Sebastian Andrzej Siewior wrote :
>> * Alexandre Belloni | 2016-01-17 03:23:14 [+0100]:
>>
>>> index 80d74c4adcbe..43b50634d640 100644
>>> --- a/drivers/clocksource/timer-atmel-pit.c
>>> +++ b/drivers/clocksource/timer-atmel-pit.c
>>> @@ -96,11 +96,44 @@ static int pit_clkevt_shutdown(struct clock_event_device *dev)
>>>
>>> 	/* disable irq, leaving the clocksource active */
>>> 	pit_write(data->base, AT91_PIT_MR, (data->cycle - 1) | AT91_PIT_PITEN);
>>> -	free_irq(atmel_pit_irq, data);
>>> +	if (!clockevent_state_detached(dev))
>>> +		free_irq(data->irq, data);
>>
>> I did it in the meantime without clockevent_state_detached(). From what
>> it looks, it first sets the state and then invokes
>> pit_clkevt_shutdown(). Any particular reason for this?
>>
> 
> Yeah, I forgot to mention that. Freeing the irq unconditionally
> results in:
…

> 
> 
> My understanding is that clockevents_exchange_device() changes the state
> from detached to shutdown and so at that point the IRQ has never been
> requested.

I see. So we get shutdown called twice while set_periodic was only
called once. In that case I would suggest to have internal bookkeeping
instead of relying on current core's behavior when it is time free the
irq.

> 

Sebastian