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Subject: Re: [PATCH v2 1/4] gpio: gpiolib: Allow GPIO IRQs to lazy disable
To:     Stephen Boyd <swboyd@chromium.org>, bjorn.andersson@linaro.org,
        evgreen@chromium.org, linus.walleij@linaro.org, maz@kernel.org,
        mka@chromium.org
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        linux-gpio@vger.kernel.org, agross@kernel.org, tglx@linutronix.de,
        jason@lakedaemon.net, dianders@chromium.org, rnayak@codeaurora.org,
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References: <1590253873-11556-1-git-send-email-mkshah@codeaurora.org>
 <1590253873-11556-2-git-send-email-mkshah@codeaurora.org>
 <159057264232.88029.4708934729701385486@swboyd.mtv.corp.google.com>
From:   Maulik Shah <mkshah@codeaurora.org>
Message-ID: <4e070cda-8c22-c554-610e-172320045840@codeaurora.org>
Date:   Wed, 27 May 2020 16:56:14 +0530
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Hi,

On 5/27/2020 3:14 PM, Stephen Boyd wrote:
> 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")
Thanks for pointing this, i will address in next revision.
>
>> 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(-)
>>
>> 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.

Thanks,
Maulik
>
>> +}
>> +
>> +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);
>> +}
>> +

-- 
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