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

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Message-ID: <159057264232.88029.4708934729701385486@swboyd.mtv.corp.google.com>
Date:   Wed, 27 May 2020 02:44:02 -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,
        Maulik Shah <mkshah@...eaurora.org>
Subject: Re: [PATCH v2 1/4] gpio: gpiolib: Allow GPIO IRQs to lazy disable

Quoting Maulik Shah (2020-05-23 10:11:10)
> With 'commit 461c1a7d4733 ("gpiolib: override irq_enable/disable")' gpiolib
> overrides irqchip's irq_enable and irq_disable callbacks. If irq_disable
> callback is implemented then genirq takes unlazy path to disable irq.
> 
> Underlying irqchip may not want to implement irq_disable callback to lazy
> disable irq when client drivers invokes disable_irq(). By overriding
> irq_disable callback, gpiolib ends up always unlazy disabling IRQ.
> 
> Allow gpiolib to lazy disable IRQs by overriding irq_disable callback only
> if irqchip implemented irq_disable. In cases where irq_disable is not
> implemented irq_mask is overridden. Similarly override irq_enable callback
> only if irqchip implemented irq_enable otherwise irq_unmask is overridden.
> 
> Fixes: 461c1a7d47 (gpiolib: override irq_enable/disable)

This isn't a proper Fixes line. Should have quotes

Fixes: 461c1a7d4733 ("gpiolib: override irq_enable/disable")

> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
> ---
>  drivers/gpio/gpiolib.c      | 55 +++++++++++++++++++++++++++++----------------
>  include/linux/gpio/driver.h | 13 +++++++++++
>  2 files changed, 49 insertions(+), 19 deletions(-)
> 
> 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?

> +}
> +
> +static void gpiochip_irq_unmask(struct irq_data *d)
> +{
> +       struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
> +
> +       gpiochip_enable_irq(gc, d->hwirq);
> +       if (gc->irq.irq_unmask)
> +               gc->irq.irq_unmask(d);
> +}
> +