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

[Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>]

Hello Bartosz,

On Thu, Nov 08, 2018 at 06:07:43PM +0100, Bartosz Golaszewski wrote:
> czw., 13 wrz 2018 o 11:13 Linus Walleij <linus.walleij@xxxxxxxxxx> napisał(a):
> >
> > 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.
> >
> 
> Hi Linus, Uwe,
> 
> just FYI - this patch broke existing libgpiod tests in 4.20-rc1.
> 
> With this change, if user space requests a line for events of specific
> type, let's say rising edge, both falling and rising edge events will
> be emitted as rising edge.

I bet this is using the gpio-mockup driver. The problem is that the
mockup driver fires an irq for each write independent of the sensitivity
configured by the consumer.

Best regards
Uwe

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