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

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Date:	Tue, 24 Mar 2015 17:06:30 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Lars-Peter Clausen <lars@...afoo.de>,
	Robert Dolca <robert.dolca@...il.com>,
	Robert Dolca <robert.dolca@...el.com>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Peter Meerwald <pmeerw@...erw.net>,
	Denis CIOCCA <denis.ciocca@...com>
Subject: Re: [PATCH] IIO: Adds ACPI support for ST gyroscopes

On Tue, Mar 24, 2015 at 02:57:49PM +0100, Linus Walleij wrote:
> On Tue, Mar 24, 2015 at 2:38 PM, Lars-Peter Clausen <lars@...afoo.de> wrote:
> > On 03/24/2015 02:26 PM, Robert Dolca wrote:
> >> On Tue, Mar 24, 2015 at 2:17 PM, Lars-Peter Clausen <lars@...afoo.de>
> >> wrote:
> 
> >> In the ACPI description you specify one or more IRQ GPIO pins. In the
> >> driver you request the GPIO pin using the index. In the ACPI 5.1
> >> specification you can use named GPIOs instead of index.
> >
> >
> > But is there a way to distinguish between IRQ GPIOs and non IRQ GPIOs? If it
> > is clear that a certain GPIO is the IRQ for the device the I2C framework
> > should take care of assigning the client->irq field, instead of doing it
> > manually in each and every device driver.
> 
> In the device tree case we have a mechanism where each
> GPIO chip implements two API:s, one gpio_chip API and
> one irqchip API.
> 
> Then in the tree both the GPIO and IRQs can be assigned as
> resources to clients, orthogonally. Usually this will only work
> if there is a 1-to-1 correspondence between the GPIO lines
> and available IRQ line triggers on the GPIO chip, but that is
> indeed the most common. They will then usually also have
> the same line offset numbers. In some odd cases I guess it
> won't work this way.
> 
> The I2C subsystem does this for the device tree case in
> i2c_device_probe() like this:
> 
>  if (!client->irq && dev->of_node) {
>                 int irq = of_irq_get(dev->of_node, 0);
> 
>                 if (irq == -EPROBE_DEFER)
>                         return irq;
>                 if (irq < 0)
>                         irq = 0;
> 
>                 client->irq = irq;
>         }
> 
> This is why the code does not contain any OF/DT
> IRQ assignment code.
> 
> However in the ACPI probe path I guess it doesn't
> happen then?

In ACPI we have two kind of GPIOs: GpioIo and GpioInt. The latter is
used to describe GPIOs that can be used as interrupts.

In order to translate a GpioInt to an interrupt number we would need to
request the GPIO first here (in the I2C core), call gpiod_to_irq() to it
and assign that to the client->irq.

This has few problems that I have not yet figured out. Maybe someone
here can suggest what to do:

 1) Who is responsible in releasing the GPIO?
 2) What if the driver wants to use that pin as a GPIO instead? The GPIO
    is already requested by the I2C core.
 3) We may have multiple GpioInts for devices like GPIO button array.
    Which one we should pick, or should we let the driver to handle this
    separetely?

I recently did similar change to drivers/hid/i2c-hid/i2c-hid.c and would
be happy if we can get this factored to some generic code.
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