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    SubjectRe: [PATCH 2/2] HID: i2c-hid: Add support for GPIO interrupts
    On Tue, Jan 27, 2015 at 11:14:58AM +0000, Mark Rutland wrote:
    > On Tue, Jan 27, 2015 at 10:59:31AM +0000, Mika Westerberg wrote:
    > > On Tue, Jan 27, 2015 at 10:39:25AM +0000, Mark Rutland wrote:
    > > > > If the above is not the right way to use GPIOs as interrupt, can you
    > > > > please tell me how it is done then?
    > > >
    > > >
    > > > So lets say we have a device which generates an interrupt:
    > > >
    > > > device@f00 {
    > > > compatible = "some-interrupting-device";
    > > > reg = <0xf00 0x100>;
    > > > interrupts = < ... >;
    > > > };
    > > >
    > > > It's intended that this is connected to an interrupt controller:
    > > >
    > > > ic: interrupt-controller@b00 {
    > > > compatible = "some-interrupt-controller";
    > > > reg = <0xb00 0x100>;
    > > > #interrupt-cells = <1>;
    > > > };
    > > >
    > > > device@f00 {
    > > > compatible = "some-interrupting-device";
    > > > reg = <0xf00 0x100>;
    > > > interrupt-parent = <&ic>;
    > > > interrupts = <0x3>;
    > > > };
    > > >
    > > > But in some cases, this gets connected to a GPIO controller. In these
    > > > cases, the device is still logically generating an interrupt, and the
    > > > fact that the endpoint is an interrupt controller is irrelevant from the
    > > > PoV of the device. So we acknowledge that the GPIO controller is also
    > > > capable of acting as an interrupt controller, and mark it as such:
    > > >
    > > > gc: gpio-controller@000 {
    > > > compatible = "some-gpio-controller";
    > > > reg = <0x000 0x100>;
    > > > #gpio-cells = <1>;
    > > > #interrupt-cells = <1>;
    > > > };
    > > >
    > > > device@f00 {
    > > > compatible = "some-interrupting-device";
    > > > reg = <0xf00 0x100>;
    > > > interrupt-parent = <&gc>;
    > > > interrupts = <0x1>;
    > > > };
    > > >
    > > > Thus the device binding only describes the logical interrupt, and the
    > > > driver only needs to handle interrupts.
    > >
    > > OK.
    > >
    > > > In cases where the binding/driver actually care about the GPIO being a
    > > > GPIO (e.g. for card detect in an MMC controller), describing the GPIO as
    > > > a GPIO makes sense, and we can try gpio_to_irq as an optimisation over
    > > > polling the state of the GPIO.
    > >
    > > Well, I've seen touch panels where you actually need to switch the GPIO
    > > to be output and do some magic before you can use the same GPIO as an
    > > interrupt.
    >
    > Ok. That's a nasty case, but surely in that case the relevant GPIO
    > shoiuld be a GpioIO object for output?

    I can't remember the details anymore, possibly it was GpioIo().

    Nothing prevents you from using GpioIo() as an interrupt.

    >
    > > > > BTW, passing NULL to gpiod_get() implies property named "gpios" in DT
    > > > > (which is why I added it to the documentation).
    > > >
    > > > Sure. My concern is that we should not need to deal with GPIOs in this
    > > > case were the GPIO is only there to function as an interrupt.
    > > >
    > > > Given that GpioInt seems to describe an interrupt which happens to be
    > > > backed by a GPIO, I don't understand what it is necessary to translate
    > > > this as a GPIO rather than an interrupt. If it were going to be used as
    > > > a GPIO, then it would be a GpioIO object, no?
    > >
    > > OK, so where do you propose we handle the translation if not in the
    > > driver? Also keep in mind that some of the devices may have multiple
    > > GpioInt()s.
    >
    > To me it seems that GpioInt objects should be translated to interrupts
    > by some core code. How are interrupts described and handed in ACPI? Are
    > they resource along the lines of GpioInts, or are they a completely
    > separate class of device property?

    They are similar resources in _CRS, like GpioIo/GpioInt etc. Below is
    from another touch panel:

    Name (_CRS, ResourceTemplate () {
    I2cSerialBus (0x004C, ControllerInitiated, 0x00061A80,
    AddressingMode7Bit, "\\_SB.PCI0.I2C1", 0x00, ResourceConsumer,,)
    Interrupt (ResourceConsumer, Level, ActiveLow, Exclusive, ,, )
    {
    0x00000022,
    }
    })

    If we see one of the above we automatically add it to client->irq in
    case of I2C device.


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