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Subject: Re: [PATCH v2 1/4] gpio: gpiolib: Allow GPIO IRQs to lazy disable
From:   Stephen Boyd <swboyd@chromium.org>
Cc:     linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-gpio@vger.kernel.org, agross@kernel.org, tglx@linutronix.de,
        jason@lakedaemon.net, dianders@chromium.org, rnayak@codeaurora.org,
        ilina@codeaurora.org, lsrao@codeaurora.org,
        Maulik Shah <mkshah@codeaurora.org>
To:     Maulik Shah <mkshah@codeaurora.org>, bjorn.andersson@linaro.org,
        evgreen@chromium.org, linus.walleij@linaro.org, maz@kernel.org,
        mka@chromium.org
Date:   Wed, 27 May 2020 02:44:02 -0700
Message-ID: <159057264232.88029.4708934729701385486@swboyd.mtv.corp.google.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Quoting Maulik Shah (2020-05-23 10:11:10)
> With 'commit 461c1a7d4733 ("gpiolib: override irq_enable/disable")' gpiol=
ib
> overrides irqchip's irq_enable and irq_disable callbacks. If irq_disable
> callback is implemented then genirq takes unlazy path to disable irq.
>=20
> 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.
>=20
> 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.
>=20
> 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@codeaurora.org>
> ---
>  drivers/gpio/gpiolib.c      | 55 +++++++++++++++++++++++++++++----------=
------
>  include/linux/gpio/driver.h | 13 +++++++++++
>  2 files changed, 49 insertions(+), 19 deletions(-)
>=20
> 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);
>  }
> =20
> +static void gpiochip_irq_mask(struct irq_data *d)
> +{
> +       struct gpio_chip *gc =3D 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 =3D gpiod_get(...)
 unsigned int girq =3D 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 =3D irq_data_get_irq_chip_data(d);
> +
> +       gpiochip_enable_irq(gc, d->hwirq);
> +       if (gc->irq.irq_unmask)
> +               gc->irq.irq_unmask(d);
> +}
> +