Re: [PATCH] IIO: Adds ACPI support for ST gyroscopes

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

On Thu, Mar 26, 2015 at 04:37:39PM +0200, Octavian Purdila wrote:
> On Thu, Mar 26, 2015 at 4:04 PM, Mika Westerberg
> <mika.westerberg@linux.intel.com> wrote:
> > On Thu, Mar 26, 2015 at 02:04:35PM +0200, Octavian Purdila wrote:
> >> On Thu, Mar 26, 2015 at 12:16 PM, Mika Westerberg
> >> <mika.westerberg@linux.intel.com> wrote:
> >> > On Wed, Mar 25, 2015 at 11:12:16PM +0200, Octavian Purdila wrote:
> >> >> On Wed, Mar 25, 2015 at 3:21 PM, Mika Westerberg
> >> >> <mika.westerberg@linux.intel.com> wrote:
> >> >> > On Wed, Mar 25, 2015 at 02:25:05PM +0200, Mika Westerberg wrote:
> >> >> >> I think we can do the same for ACPI GpioInts so that we introduce
> >> >> >> acpi_gpio_irq_get() that translates from GpioInt to Linux IRQ
> >> >> >> numberspace. Then we can do something like below in I2C core:
> >> >> >>
> >> >> >>       if (client->irq <= 0) {
> >> >> >>               int irq = -ENOENT;
> >> >> >>
> >> >> >>                 if (dev->of_node)
> >> >> >>                         irq = of_irq_get(dev->of_node, 0);
> >> >> >>                 else if (ACPI_COMPANION(dev))
> >> >> >>                         irq = acpi_gpio_irq_get(ACPI_COMPANION(dev), 0);
> >> >> >>
> >> >> >>               if (irq == -EPROBE_DEFER)
> >> >> >>                         return irq;
> >> >> >>                 if (irq < 0)
> >> >> >>                         irq = 0;
> >> >> >>
> >> >> >>                 client->irq = irq;
> >> >> >>       }
> >> >> >>
> >> >> >> Now it has the drawback that the first GpioInt will not be available to
> >> >> >> the driver anymore (as a GPIO since it is locked) but if DT already does
> >> >> >> the same we should be fine.
> >> >> >
> >> >> > Below patch should take care of this.
> >> >> >
> >> >>
> >> >> One issue we noticed is that now the gpio request and set input
> >> >> directions operations are not called anymore. Some gpio controller
> >> >> drivers (dln2, adnp, lynx_point from quickly browsing the code) do not
> >> >> explicitly enable the GPIO pin nor set direction to input when the
> >> >> interrupt is enabled. Depending on hardware this may be an issue - it
> >> >> is on dln2 for example.
> >> >>
> >> >> Should the gpio controllers enable and set to input in irq_enable,
> >> >> irq_bus_sync_unlock, etc.? Or should this be done in gpiolib?
> >> >
> >> > Good question.
> >> >
> >> > In general I think that it is assumed that the boot firmware configures
> >> > the pin upfront. However, we have seen too many times that it actually
> >> > doesn't happen or it is configured wrong.
> >> >
> >> > Perhaps we could do this in GPIO core, for example in
> >> > gpiochip_irq_reqres/gpiochip_irq_map or so.
> >> >
> >>
> >> That sounds good to me. We tested your patch with the patch below and
> >> we can now directly use client->irq:
> >>
> >> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> >> index 568aa2b..9865627 100644
> >> --- a/drivers/gpio/gpiolib.c
> >> +++ b/drivers/gpio/gpiolib.c
> >> @@ -511,6 +511,19 @@ static const struct irq_domain_ops gpiochip_domain_ops = {
> >>  static int gpiochip_irq_reqres(struct irq_data *d)
> >>  {
> >>         struct gpio_chip *chip = irq_data_get_irq_chip_data(d);
> >> +       int ret;
> >> +
> >> +       ret = gpiod_request(&chip->desc[d->hwirq], "IRQ");
> >> +       if (ret) {
> >> +               chip_err(chip, "unable to request %lu for IRQ\n", d->hwirq);
> >> +               return ret;
> >> +       }
> >
> > What if the driver has already requested the GPIO?
> >
> 
> Initially I implemented the above to take that into account, e.g. if
> (test_and_set_bit(FLAG_REQUESTED, &desc->flags) ...
> 
> But than I thought that we can't mess up with the GPIO anyway while
> the interrupt is in use.

That's right but then the above will fail also normal cases. For example
if the driver gets the irq like:

	desc = devm_gpiod_get(dev, ..);
	gpiod_direction_input(desc);
	irq = gpiod_to_irq(desc);

	ret = request_irq(irq, ...)

at this point we end up calling gpiochip_irq_reqres() which cannot
request the GPIO again and fails.

> One case I missed was if the user wants to read the GPIO while using
> it as an interrupt which seems to be possible...

While the GPIO is locked as IRQ it cannot be done as far as I can tell
but you can work it around by calling free_irq() first.

> 
> >> +
> >> +       ret = gpiod_direction_input(&chip->desc[d->hwirq]);
> >> +       if (ret) {
> >> +               chip_err(chip, "unable to set HW IRQ %lu as input\n", d->hwirq);
> >> +               return ret;
> >> +       }
> >>
> >>         if (gpiochip_lock_as_irq(chip, d->hwirq)) {
> >>                 chip_err(chip,