linux-kernel - Re: [PATCH v2 1/4] gpio: gpiolib: Allow GPIO IRQs to lazy disable

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Message-ID: <159062812628.69627.2153485337510882984@swboyd.mtv.corp.google.com>
Date:   Wed, 27 May 2020 18:08:46 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Maulik Shah <mkshah@...eaurora.org>, bjorn.andersson@...aro.org,
        evgreen@...omium.org, linus.walleij@...aro.org, maz@...nel.org,
        mka@...omium.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-gpio@...r.kernel.org, agross@...nel.org, tglx@...utronix.de,
        jason@...edaemon.net, dianders@...omium.org, rnayak@...eaurora.org,
        ilina@...eaurora.org, lsrao@...eaurora.org
Subject: Re: [PATCH v2 1/4] gpio: gpiolib: Allow GPIO IRQs to lazy disable

Quoting Maulik Shah (2020-05-27 04:26:14)
> On 5/27/2020 3:14 PM, Stephen Boyd wrote:
> > Quoting Maulik Shah (2020-05-23 10:11:10)
> >> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> >> index eaa0e20..3810cd0 100644
> >> --- a/drivers/gpio/gpiolib.c
> >> +++ b/drivers/gpio/gpiolib.c
> >> @@ -2465,32 +2465,37 @@ static void gpiochip_irq_relres(struct irq_data *d)
> >>          gpiochip_relres_irq(gc, d->hwirq);
> >>   }
> >>   
> >> +static void gpiochip_irq_mask(struct irq_data *d)
> >> +{
> >> +       struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
> >> +
> >> +       if (gc->irq.irq_mask)
> >> +               gc->irq.irq_mask(d);
> >> +       gpiochip_disable_irq(gc, d->hwirq);
> > How does this work in the lazy case when I want to drive the GPIO? Say I
> > have a GPIO that is also an interrupt. The code would look like
> >
> >   struct gpio_desc *gpio = gpiod_get(...)
> >   unsigned int girq = gpiod_to_irq(gpio)
> >
> >   request_irq(girq, ...);
> >
> >   disable_irq(girq);
> >   gpiod_direction_output(gpio, 1);
> >
> > In the lazy case genirq wouldn't call the mask function until the first
> > interrupt arrived on the GPIO line. If that never happened then wouldn't
> > we be blocked in gpiod_direction_output() when the test_bit() sees
> > FLAG_USED_AS_IRQ? Or do we need irqs to be released before driving
> > gpios?
> 
> The client driver can decide to unlazy disable IRQ with below API...
> 
>   irq_set_status_flags(girq, IRQ_DISABLE_UNLAZY);
> 
> This will immediatly invoke mask function (unlazy disable) from genirq, 
> even though irq_disable is not implemented.
> 

Sure a consumer can disable the lazy feature, but that shouldn't be
required to make this work. The flag was introduced in commit
e9849777d0e2 ("genirq: Add flag to force mask in
disable_irq[_nosync]()") specifically to help devices that can't disable
the interrupt in their own device avoid a double interrupt.