Re: [PATCH v11 6/8] platform: cznic: turris-omnia-mcu: Add support for MCU provided TRNG

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Thu, Jun 06, 2024 at 10:53:08AM +0200, Marek Behún wrote:
> On Wed, 5 Jun 2024 22:00:20 +0300
> Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> 
> > > +       irq_idx = omnia_int_to_gpio_idx[__bf_shf(OMNIA_INT_TRNG)];
> > > +       irq = gpiod_to_irq(gpiochip_get_desc(&mcu->gc, irq_idx));
> > > +       if (irq < 0)
> > > +               return dev_err_probe(dev, irq, "Cannot get TRNG IRQ\n");  
> > 
> > Okay, it's a bit more complicated than that. The gpiochip_get_desc()
> > shouldn't be used. Bart, what can you suggest to do here? Opencoding
> > it doesn't sound to me a (fully) correct approach in a long term.
> 
> Note that I can't use gpiochip_request_own_desc(), nor any other
> function that calls gpio_request_commit() (like gpiod_get()), because
> that checks for gpiochip_line_is_valid(), and this returns false for
> the TRNG line, cause that line is not a GPIO line, but interrupt only
> line.
> 
> That is why I used
>   irq = irq_create_mapping(dev, mcu->gc.irq.domain, irq_idx);
> until v7, with no reference to gpio descriptors, since this line is not
> a GPIO line.
> 
> We have discussed this back in April, in the thread
>   https://lore.kernel.org/soc/20240418121116.22184-8-kabel@kernel.org/
> where we concluded that
>   irq = gpiod_to_irq(gpiochip_get_desc(gc, irq_idx));
> is better...

That's fine to not use other APIs, the problem here is with reference counting
on the GPIO device. The API you could use is gpio_device_get_desc(). But you
need to have a GPIO device pointer somewhere in your driver being available.

-- 
With Best Regards,
Andy Shevchenko