gpio ->to_irq

gpio ->to_irq

[Dvorkin Dmitry]

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Hello!

I have a question about gpiochip ->to_irq().

Kernel call gpio_to_irq() requests IRQ for the pin, previously taken by 
*gpio_request().

But for sysfs when user does echo "pin#" > /sys/class/gpio/export  
gpio_to_irq() is also called at the time of export there:

https://elixir.bootlin.com/linux/v5.4.100/source/drivers/gpio/gpiolib-sysfs.c#L171

and there

https://elixir.bootlin.com/linux/v5.4.100/source/drivers/gpio/gpiolib-sysfs.c#L378

It is a problem for my driver. I have 120 pins and only 7 dynamically 
muxed GPIO irqs.

So when somebody requests gpio_to_irq() I am creating the mux to the 
first free gpio IRQ. But When user just exports GPIO pin using "old" 
sysfs kernel interface in the filesystem, it should not be done.

How can I see if gpio_to_irq() has been called by sysfs to prevent 
unnecessary dynamic muxing? Or there another way to get rid of this 
wrong behavior in my driver?


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Re: gpio ->to_irq

[Andy Shevchenko]

On Wed, May 11, 2022 at 12:03 PM Dvorkin Dmitry <dvorkin@tibbo.com> wrote:
>
> Hello!
>
> I have a question about gpiochip ->to_irq().
>
> Kernel call gpio_to_irq() requests IRQ for the pin, previously taken by
> *gpio_request().
>
> But for sysfs when user does echo "pin#" > /sys/class/gpio/export
> gpio_to_irq() is also called at the time of export there:
>
> https://elixir.bootlin.com/linux/v5.4.100/source/drivers/gpio/gpiolib-sysfs.c#L171
>
> and there
>
> https://elixir.bootlin.com/linux/v5.4.100/source/drivers/gpio/gpiolib-sysfs.c#L378
>
> It is a problem for my driver.

It's much easier to answer if you may share the source code of your
driver. Ideally if there is a publicly available datasheet on the
hardware in question.

> I have 120 pins and only 7 dynamically
> muxed GPIO irqs.
>
> So when somebody requests gpio_to_irq() I am creating the mux to the
> first free gpio IRQ. But When user just exports GPIO pin using "old"
> sysfs kernel interface in the filesystem, it should not be done.
>
> How can I see if gpio_to_irq() has been called by sysfs to prevent
> unnecessary dynamic muxing? Or there another way to get rid of this
> wrong behavior in my driver?

Generally speaking nobody should call gpio_to_irq() in the new code.
This is a legacy interface that mustn't be used.

-- 
With Best Regards,
Andy Shevchenko