Re: [PATCH v1 5/5] gpio: pca953x: Override GpioInt() pin for Intel Galileo Gen 2

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Mon, May 25, 2020 at 04:01:08PM +0300, Andy Shevchenko wrote:
> On Mon, May 25, 2020 at 03:21:36PM +0300, Mika Westerberg wrote:
> > On Mon, May 25, 2020 at 02:35:51PM +0300, Andy Shevchenko wrote:
> > > On Mon, May 25, 2020 at 02:05:56PM +0300, Mika Westerberg wrote:
> > > > On Mon, May 25, 2020 at 01:13:35PM +0300, Andy Shevchenko wrote:
> > > > > Due to parsing of ACPI tables. I don't want to copy'n'paste 25% of
> > > > > gpiolib-acpi.c in here. I think provided solution is cleaner and (more)
> > > > > flexible in terms of maintenance.
> > > > 
> > > > Hmm, you seem to pass a hard-coded pin number (1) to the core that then
> > > > passes it back to the driver. Why you can't simple use that number here
> > > > directly? You don't need to parse anything. What I'm missing? :-)
> > > 
> > > Okay, so, AFAIU you are proposing something like this:
> > > 
> > > 1) find a GPIO controller by the ACPI path (somehow, I guess by finding a
> > >    handle followed by physical device behind it); 2) somehow to request a
> > >    pin from that device by number;
> > > 3) convert to IRQ and use.
> > > 
> > > Is it correct?
> > 
> > Well, no. In the first patch you do this:
> > 
> >   pin = lookup->info.quirks_data;
> > 
> > and this essentially becomes 1 so you know the pin number upfront in the
> > driver. Why not simply get GPIO number 1 in the driver and use it as an
> > interrupt? You know already that this particular board with the matching
> > DMI identifier always uses the this number anyway.
> 
> But GPIO (relative!) number is not enough. We need to understand more, i.e.:
> 1) from which GPIO controller it comes from (okay, for this particular platform I know it);
> 2) which expander does have this resource (they all have same ACPI HID).
> 
> So, second one means to count GpioInt() resources (I don't remember if we have
> helper for that, probably we can add one). For the first we need to get a GPIO
> controller something (gpiochip?) And this first one I have no idea how we can
> perform without talking to the core.
> 
> Basically, it may be done by reimplementing acpi_dev_gpio_irq_get(), followed
> by acpi_get_gpiod_by_index(), followed by acpi_gpio_resource_lookup(), followed
> by acpi_populate_gpio_lookup(), where at last this quirk should be applied.
> 
> It seems for me like an over duplicated solution.
> 
> I really don't understand how we can shortcut all these. What am I missing?

Why for example following would not work? If it is using global GPIO numbers
anyway.

static int pca953x_acpi_interrupt_get_irq(struct device *dev)
{
        struct gpio_desc *desc;                                                          
 
        desc = gpio_to_desc(1);
        if (!desc)
                return -ENODEV;

        return gpiod_to_irq(desc);
}