unexpected side effect of "gpiolib: override irq_enable/disable"

Hans Verkuil hverkuil at xs4all.nl
Fri Sep 14 01:24:56 PDT 2018


On 09/13/2018 11:02 AM, Ludovic Desroches wrote:
> On Thu, Sep 13, 2018 at 10:42:49AM +0200, Hans Verkuil wrote:
>> On 09/13/18 09:47, Ludovic Desroches wrote:
>>> Hi Hans,
>>>
>>> On Wed, Sep 12, 2018 at 05:30:35PM +0200, Hans Verkuil wrote:
>>>> Hi Ludovic,
>>>>
>>>> On 09/12/2018 04:58 PM, Ludovic Desroches wrote:
>>>>> Hi,
>>>>>
>>>>> Using next-20180912, my kernel hangs during the boot. Git bisect tell me
>>>>> that the cause of my issue is the commit "gpiolib: override
>>>>> irq_enable/disable"
>>>>>
>>>>> I dug further and this patch can have some side effects. When booting, I
>>>>> have an infinite loop when trying to enable a gpio irq. I don't know if
>>>>> the pinctrl-at91 driver is the only one concerned or not.
>>>>>
>>>>> The pattern leading to this issue is quite simple: we have several gpio
>>>>> controllers sharing the same irq_chip structure. Installing the
>>>>> irq_enable/irq_disable hook works well the first time. The second time,
>>>>> since the irq_enable has been altered to use gpiochip_irq_enable,
>>>>> this latest function will call itself again and again by calling
>>>>> irq_enable.
>>>>>
>>>>> I think it should be better to have one irq_chip structure per gpio
>>>>> controller. I am going to do a patch for pinctrl-at91. Excepting if you
>>>>> think it has to be solved in a different way.
>>>>>
>>>>>
>>>>> Ludovic
>>>>>
>>>>
>>>> Can you try this patch first?
>>>
>>> Yes it works, I also have this kind of change in mind.
>>
>> Good. I think this patch needs to go in regardless, since this makes it
>> a lot more robust. My main question is whether this situation is indicative
>> of a bad driver design, or if this is normal behavior that this code just
>> has to support.
>>
>>> I am not sure which solution is the best. Of course I prefer this one as
>>> I don't have to modify the pinctrl-at91 driver but if I have to modify
>>> it to not share the same irq_chip structure, I'll handle it. Just let me
>>> know.
>>
>> I tried to figure out where this happens exactly in this driver (sharing the
>> same irq_chip structure), but I'm not quite sure I fully understand it. Can
>> you point out where this happens?
>>
> 
> There are 5 instances of the gpio controller (A, B, C, D, E) and they all use
> the same irqchip since the behaviour is common.
> 
> When adding A as a gpiochip_irqchip (in at91_gpio_of_irq_setup()), we set the
> hooks so:

Ah, now I see: gpio_irqchip is a static struct. That's the bit I missed when I
looked at the code earlier.

Thanks,

	Hans



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