Re: [PATCH] gpiolib: don't support irq sharing for gpio edge detection

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Aug 20, 2018 at 8:32 AM Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:

> Trying to work out the right event if it's not sure that the examined
> gpio actually moved is impossible.

I applied the patch with the following reasoning.

1) Uwe has a usecase and hardware that needs this so he can do
what he needs to do. I.e. the patch corresponds to a practical need
of a user.

2) Only theoretical counter-arguments.

3) Uwe clarified that it is fine to put IRQ sharing back if/when
we support level-triggered IRQs from userspace. This makes a
lot of sense to me.

4) Rough consensus and running code.

I edited the subject and commit message to reflect that we are talking
about the userspace events here, not in-kernel users.

Edge triggers are tricky and I feel a bit uncertain about how we handle
all kinds of electronics out there. I can think about a few design
mistakes.

At one point I had the feeling level interrupts on GPIO lines are
completely bogus, but I guess they make some sense for an
intelligent peripheral (like on I2C) with it own internal status
register that you then go and handle in a thread.

Yours,
Linus Walleij