Re: [libgpiod][PATCH 3/7] tests: event: extend test coverage for reading multiple line events at once

[Bartosz Golaszewski <brgl@xxxxxxxx>]

czw., 19 gru 2019 o 15:36 Kent Gibson <warthog618@xxxxxxxxx> napisał(a):
>
> > > >
> > > > I'm not sure I understand. We can't have two event fd's for the same
> > > > line. Or are you thinking about setting up a second line, generating
> > > > events on it and consuming them so that we can rely on the timing to
> > > > make sure the events were registered for the first one too?
> > > >
> > >
> > > I was thinking of two event fds on the one line, and you are
> > > correct, there can only be one, so that wont work.
> > > Wrt using two lines, I'm not sure ordering can be guaranteed as you
> > > end up with two separate debugfs writes...
> > >
> >
> > Yeah I gave it a spin and it turns out it's not reliable - some events
> > still get dropped albeit less than without any syncing. The usleep()
> > calls are still better than this. Any other ideas? I agree this is not
> > optimal, but couldn't come up with anything else.
> >
>
> The two options I can think of are getting the debugfs write
> to block until the simulated interrupt has been serviced, or adding a
> multi-line set to the mockup so the two lines can be set simultaneously.
> I'm not sure the first is possible.
> And the second wont help if it results in two interrupts unless the
> order the interrupts are serviced is guaranteed.
> Either way it seems like a whole lot of work just to remove the sleeps,
> so the sleeps seem like a reasonable workaround :(.
>

Now when I looked at gpio-mockup again I'm under the impression that
the interrupt should be fired from the set() callback, not from the
debugfs write callback. But this is a minor detail and it won't help
here.

Anyway, I'm really not sure how to do it any differently. We can also
be less strict in user-space - we can schedule, let's say, 16 events
without sleeps and not really verify the number of read events - just
check if it's bigger than 1 and that what we read are actual events
(valid event_type).

Bart