Re: how to request gpiochip line which is only valid as an interrupt?

["Marek Behún" <kabel@kernel.org>]

Dear Andy,

On Wed, 12 Jun 2024 10:55:55 +0200
Marek Behún <kabel@kernel.org> wrote:

> Originally, I used the low-level irq_create_mapping(), passing it the
> gpiochip's IRQ domain, something like:
> 
>   irq =  irq_create_mapping(mcu->gc.irq.domain, TRNG_HWIRQ);
> 
> Andy said [1] that
> 
>   This looks like some workaround against existing gpiod_to_irq(). Why
>   do you need this?
> 
> I should not poke into gpiolib's internals like that.
> 
> So I changed it to
> 
>   irq = gpiod_to_irq(gpiochip_get_desc(&mcu->gc, TRNG_HWIRQ));

I think the original code 

  irq = irq_create_mapping(mcu->gc.irq.domain, TRNG_HWIRQ);

should be used. The trng part of the driver is interested in the
interrupt, it does not care if the interrupt is provided via a GPIO
chip.

The mcu device is a gpio-controller, but also an interrupt-controller.
That the interrupts are provided via gpiolib is irrelevant.

So I think that what we did back in April, changing to gpiod_to_irq(),
is not actually correct, from semantic point of view.

For example if some other driver wanted to use a MCU interrupt, it
would have simply used:
  of_get_irq()
not referring to gpio descriptors at all, i.e. not something like
  gpiod_to_irq(gpiod_find_and_request())

(I do actually have code prepared for another driver that will use
an interrupt provided by the MCU.)

What do you think?

Marek