From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Tony He <huangya90@gmail.com>, kernelnewbies@kernelnewbies.org
Subject: Re: GPIO and interrupt
Date: Wed, 26 Jul 2023 13:09:09 +0200 [thread overview]
Message-ID: <fcf9b4ed-cd26-7632-4998-5be1ff9808b2@pengutronix.de> (raw)
In-Reply-To: <CAAUX2SXaim8FFKKmKJyuBXWnZrTXspioL4iNn3h5aVyLDoLFFQ@mail.gmail.com>
Hello Tony,
On 26.07.23 12:10, Tony He wrote:
> Hi,
>
> I'm writing button driver. The button is based on GPIO.When the button
> is pressed or released, the interrupt is generated. According to the
> GPIO value(1 or 0) , I can know which action is taken(pressed or
> released).
> However, a question occurred to me. Do I need to consider when to get
> the GPIO value? I mean is it possible that GPIO value will be changed
> caused by another interrupt when I get the GPIO value in top or bottom
> half
> of first interrupt? I know the CPU is fast and pushing/releasing
> button is slow, so it should not happen in practice. But let's just
> consider this case in theory. You can assume the button is pushed or
> released very very fast.
This is not only a theoretical issue. The transition from button being
pressed to unpressed and back is not noise free, so a naive translation
of IRQ/GPIO state to input events may not be sufficient.
Dealing with this is called debouncing and involves taking multiple
samples before signalling the input event.
> Seems that GPIO interrupt is special comparing with other device with
> cache. There is no cache to store data(GPIO value) for GPIO. Right?
> Can someone help to clarify this question? Thanks a lot.
IRQ handlers have a second argument with a pointer to device specific data.
You can store information there and many drivers do so. You need to take
care that the data isn't accessed concurrently though, e.g. via a spinlock.
You can see how all this is implemented in the Linux gpio_keys driver.
Cheers,
Ahmad
>
> Tony
>
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prev parent reply other threads:[~2023-07-26 11:09 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-26 10:10 GPIO and interrupt Tony He
2023-07-26 11:09 ` Ahmad Fatoum [this message]
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