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

[Kent Gibson <warthog618@xxxxxxxxx>]

On Thu, Dec 19, 2019 at 02:48:48PM +0100, Bartosz Golaszewski wrote:
> czw., 19 gru 2019 o 14:35 Kent Gibson <warthog618@xxxxxxxxx> napisał(a):
> >
> > > +
> > > +     ret = gpiod_line_request_both_edges_events(line, GPIOD_TEST_CONSUMER);
> > > +     g_assert_cmpint(ret, ==, 0);
> > > +
> > > +     gpiod_test_chip_set_pull(0, 4, 1);
> > > +     usleep(10000);
> > > +     gpiod_test_chip_set_pull(0, 4, 0);
> > > +     usleep(10000);
> > > +     gpiod_test_chip_set_pull(0, 4, 1);
> > > +     usleep(10000);
> > > +
> >
> > I assume the sleep is to wait for the event to be generated from the
> > call gpiod_test_chip_set_pull, which is not guaranteed to occur before
> > the call returns, otherwise you can toggle the line too fast and may
> > miss events.
> 
> Yes, this is why I put it there. Otherwise, some simulated interrupts
> were being dropped when they fired while the previous ones were still
> served.
> 
> > Arbitrary sleeps in code, including tests, should be avoided as they
> > are brittle and obsure what you are actually waiting for.
> 
> Indeed.
> 
> > An alternative in this case is to add a second event fd and wait for
> > the event to arrive there before continuing.
> >
> 
> 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...

Kent.