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[220.235.124.2]) by smtp.gmail.com with ESMTPSA id o98sm6905764pjb.15.2019.12.19.06.05.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Dec 2019 06:05:24 -0800 (PST) Date: Thu, 19 Dec 2019 14:05:18 +0000 From: Kent Gibson To: Bartosz Golaszewski Cc: Bartosz Golaszewski , Linus Walleij , Andy Shevchenko , linux-gpio Subject: Re: [libgpiod][PATCH 3/7] tests: event: extend test coverage for reading multiple line events at once Message-ID: <20191219140518.GA12078@firefly> References: <20191218142449.10957-1-brgl@bgdev.pl> <20191218142449.10957-4-brgl@bgdev.pl> <20191219133502.GA12028@firefly> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Thu, Dec 19, 2019 at 02:48:48PM +0100, Bartosz Golaszewski wrote: > czw., 19 gru 2019 o 14:35 Kent Gibson 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.