linux-kernel - Re: [PATCH] extcon: gpio: Request reasonable interrupts

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Message-ID: <547eacd4-e4b9-e9a9-9f89-aa33b05cb674@samsung.com>
Date:   Mon, 24 Jun 2019 09:10:58 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH] extcon: gpio: Request reasonable interrupts

On 19. 6. 8. 오전 6:24, Linus Walleij wrote:
> On Tue, Jun 4, 2019 at 3:30 AM Chanwoo Choi <cw00.choi@...sung.com> wrote:
>> On 19. 5. 31. 오전 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