linux-kernel - Re: [PATCH v2 3/9] irq/irq_sim: provide irq_sim_fire

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Date:   Tue, 12 Feb 2019 12:05:01 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Linus Walleij <linus.walleij@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/9] irq/irq_sim: provide irq_sim_fire_type()

On Tue, Feb 12, 2019 at 10:27:54AM +0000, Marc Zyngier wrote:
> On 12/02/2019 09:19, Bartosz Golaszewski wrote:
> > When userspace wants to monitor GPIO line interrupts, the GPIO
> > framework requests a threaded interrupt with IRQF_TRIGGER_FALLING,
> > IRQF_TRIGGER_RISING or both. The testing module tries to act like real
> > hardware and so if we pass only one of the *_TRIGGER_* flags, we want
> > the simulated interrupt of corresponding type to be fired.
> 
> Well, that's not how HW works.

I cannot follow. I agree with Bartosz here. If you configure your SoC's
irq-controller to only fire on a raising edge, you don't get an event
when the line falls.
 
> > Another solution - if you don't like this one -  would be to have more
> > specialized functions: irq_sim_fire_rising() and
> > irq_sim_fire_falling(). How about that?
> 
> I think you're missing the point. So far, your API has been "an
> interrupt has fired", no matter what the trigger is, and that's fine.
> That's just modeling the output of an abstract interrupt controller into
> whatever the irqsim is simulating.
> 
> Now, what you're exposing is "this is how the line changed". Which is an
> entirely different business, as you're now exposing the device output
> line. Yes, you can model it with raising/falling, but you need at least
> resampling for level interrupts, and actual edge detection (raising
> followed by raising only generates a single interrupt, while
> raising-falling-raising generates two).

This matches my concern and that's why I suggested somewhere else in
this thread to put the configuration of the sensitiveness and the actual
tracking of the line in the same component (either irqsim or
gpio-mockup). Given that there are only two irqsim users and the other
one (something in iio) doesn't need that sensitiveness stuff (and I
cannot imagine another user of irqsim with the sensitiveness support) I
think it is best to move this to the mockup driver. That's how "normal"
hardware drivers have to do it, too.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |