From mboxrd@z Thu Jan  1 00:00:00 1970
From: ulf.samuelsson@atmel.com (Ulf Samuelsson)
Date: Sat, 27 Mar 2010 01:41:52 +0100
Subject: request_irq in I2C driver causes kernel to freeze during	probe,
	but if done later - no problem!
In-Reply-To: <4BAD4FDE.2010904@atmel.com>
References: <4BAD406A.7070208@atmel.com>	<20100326232421.GG29179@n2100.arm.linux.org.uk>
	<4BAD4FDE.2010904@atmel.com>
Message-ID: <4BAD5450.7020605@atmel.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Ulf Samuelsson skrev:
> Russell King - ARM Linux skrev:
>> On Sat, Mar 27, 2010 at 12:16:58AM +0100, Ulf Samuelsson wrote:
>>> If the interrupt is executing, then we would see some I2C communication
>>> as a result, but we do not see this, before the kernel freezes.
>>>
>>> The interrupt is (and should be) called on the falling edge of the
>>> interrupt.
>>>
>>> I am currently scratching my head, and need help with ideas...
>> Do you always return IRQ_HANDLED from this handler, or do you return
>> IRQ_NONE if it does no work?
>>
>> If you always return IRQ_HANDLED even if no work was done, it could be
>> that you're spinning on this interrupt, and because you're returning
>> IRQ_HANDLED, the core interrupt handling code thinks progress is being
>> made.
>>
>> If you return IRQ_NONE, then the "bad IRQ" detection code will kick in
>> and disable the IRQ, which should result in some further progress.
>>
> 
> Thanks for fast reply.
> 
> This is my interrupt routine, which always return IRQ_HANDLED.
> sysfs shows that "mxt->invalid_irq_counter" is never incremented
> even after I successfully enable the interrupt in sysfs.
> 
> mxt->dwork will always access the I2C bus but we dont see that.
> 
> static irqreturn_t mxt_irq_handler(int irq, void *_mxt)
> {
> 	struct	mxt_data *mxt = _mxt;
> 	unsigned long	flags;
> 	mxt->irq_counter++;
> 	spin_lock_irqsave(&mxt->lock, flags);
> 
> 	if (mxt_valid_interrupt()) {
> 		/* Macro, always returning 1  on these boards */
> 		cancel_delayed_work(&mxt->dwork);
> 		schedule_delayed_work(&mxt->dwork, 0);
> 		mxt->valid_irq_counter++;
> 	} else {
> 		mxt->invalid_irq_counter++;
> 	}
> 	spin_unlock_irqrestore(&mxt->lock, flags);
> 
> 	return IRQ_HANDLED;
> }
> 

I tried doing an I2C transfer inside the interrupt routine
(this is my only way of logging)
and then the I2C probe routine locked up already when
doing the request_irq.


I do not know a lot about the internals of  "schedule_delayed_work"
at the moment - Have to start digging I guess.
I have assumed so far, that if this is called,then mxt->dwork will be
executed.

Can it be so, that nothing happens and the situation you describe
above occur?

The interrupt line will, after asserted low, remain low
until a status register is read over the I2C bus,
and the interrupt is triggered by falling edge
so I assume that the interrupt should only be called once.

If the interrupt is enabled by the register_irq, and it does
occur during the probe, and not afterwards,
can this affect the mxt_worker routine?

The probe does a significant amount of i2c communication
after the register_irq, and if the interrupt has been asserted
already, the interrupt will be deasserted before the probe exits.

Somehow I have a feeling that the freeze occurs because
the kernel wants to process the delayed work, sometimes
after the probe exits.

Maybe the i2c communication should occur before the register irq?

BR
Ulf Samuelsson


> 
> I do
> 	INIT_DELAYED_WORK(&mxt->dwork, mxt_worker);
> 	spin_lock_init(&mxt->lock);
> 
> before I request the irq
> 
> 
> BR
> Ulf Samuelsson.
> 
> 
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