Re: [PATCH] gpio/mxs: support irqs triggered by both edges

[Grant Likely <grant.likely@xxxxxxxxxxxx>]

On Mon, Mar 12, 2012 at 11:02 AM, Enrico Scholz
<enrico.scholz@xxxxxxxxxxxxxxxxx> wrote:
> Grant Likely <grant.likely@xxxxxxxxxxxx> writes:
>
>>> iMX28 silicon does not support irqs triggered by both gpio edges. Patch
>>> emulates this behavior by configuring such irqs as level triggered and
>>> by switching polarity in the interrupt handler.
>>
>> That looks dodgy and hacky.  This will definitely miss interrupts if
>> they come in too fast.
>
> Because patch calculates the trigger from the actual level, there should
> not be missed more interrupts than with native edge-both support.

Edge interrupt controllers latch interrupt requests. so that nothing
gets missed.  Level interrupt controllers do not.  So, if the irq line
toggles 3 times before the handling code gets executed, then the
kernel will still only recognize 1 irq, not 3.

>> I don't like this approach.  What do you need it for?
>
> some drivers (e.g. gpio-keys, otg gpio-vbus, gpio-charger) are requesting
> gpio based interrupts with IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING
> flags.  It is not possible to use such drivers without having EDGE_BOTH
> support.
>
>
> Enrico



-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.

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