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

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Date:   Wed, 27 May 2020 16:56:14 +0530
From:   Maulik Shah <mkshah@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.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

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@...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?

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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