Re: [PATCH] extcon: gpio: Request reasonable interrupts

[Chanwoo Choi]

On 19. 6. 8. ìì 6:24, Linus Walleij wrote:
> On Tue, Jun 4, 2019 at 3:30 AM Chanwoo Choi <cw00.choi@xxxxxxxxxxx> wrote:
>> On 19. 5. 31. ìì 3:39, Linus Walleij wrote:
> 
>>> +     /*
>>> +      * It is unlikely that this is an acknowledged interrupt that goes
>>> +      * away after handling, what we are looking for are falling edges
>>> +      * if the signal is active low, and rising edges if the signal is
>>> +      * active high.
>>> +      */
>>> +     if (gpiod_is_active_low(data->gpiod))
>>> +             irq_flags = IRQF_TRIGGER_FALLING;
>>
>> If gpiod_is_active_low(data->gpiod) is true, irq_flags might be
>> IRQF_TRIGGER_LOW instead of IRQF_TRIGGER_FALLING. How can we sure
>> that irq_flags is always IRQF_TRIGGER_FALLING?
> 
> OK correct me if I'm wrong, but this is an external connector and
> the GPIO goes low/high when the connector is physically inserted.
> If it was level trigged, it would lock up the CPU with interrupts until
> it was unplugged again, since there is no way to acknowledge a
> level IRQ.
> 
> I think level IRQ on GPIOs are only used for logic peripherals
> such as ethernet controllers etc where you can talk to the peripheral
> and get it to deassert the line and thus acknowledge the IRQ.
> 
> So the way I see it only edge triggering makes sense for extcon.
> 
> Correct me if I'm wrong.

Sorry for late reply because of vacation.

Actually, I have not thought that the kind of irq_flags are fixed
according to the category of specific h/w device. Until now, as I knew,
the h/w device have to initialize the the kind of irq_flags
for each peripheral device dependency. The each vendor of peripheral device
might design the kind of the kind of irq-flags for detection.

If possible, could you provide some example on mainline kernel?

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics