On Mon, Jan 23, 2017 at 7:46 AM, Rajasekhar Pulluru <pullururajasekhar@gmail.com> wrote:
Hi,

I have a query on device tree pertaining to modelling a gpio pin as an interrupt source. 
I have searched mailing list archives and kernel documentation before posting this and couldn't get any direct solution.
(My understanding is limited and hence posting the query below:)

My SOC has a gpio controller and uart both sharing same interrupt line as specified below. 

interrupt-parent = <&gic>;

        mygpio: gpio@0x19008000 {
                compatible = "mysoc,mygpio-controller,gc";
                #address-cells = <1>;
                #size-cells = <1>;
                #gpio-cells = <2>;
                reg = gpio: <0x19008000 0x50>;
                ngpios = <12>;
                pin-offset = <4>;
                pin-base = <4>;
                irq-base = <256>; /* sw irq base for irq handlers */
                gpio-controller;
                interrupt-controller;
                interrupts = <GIC_SPI 91 IRQ_TYPE_LEVEL_HIGH>;
        };

        uart0: serial@0x19000300 {
                compatible = "snps,dw-apb-uart";
                reg = <0x19000300 0x100>;
                interrupts = <GIC_SPI 91 IRQ_TYPE_LEVEL_HIGH>;
                clock-frequency = <62500000>;
        };

gpio pin 0 of mygpio is used as an interrupt source for detecting the presence of external pluggable device (that is not driven by kernel). 
And I intend to detect the presence of the pluggable device from user space by means of generic uio platform driver using below device

What do you intend to achieve by detecting device in userspace?
You can directly get notification using udev notification.

However, you need to send udev notification from a kernel driver.
 

        user_io@0 {
            compatible = "mydevice,generic-uio,ui_pdrv";
            status = "okay";
            interrupt-parent = <&mygpio>;
            interrupts = <0 IRQ_TYPE_LEVEL_HIGH>;
        };

Running modprobe uio_pdrv_genirq of_id="mydevice,generic-uio,ui_pdrv" and creating /dev/uio0 using mknod (major number from cat /proc/devices | grep uio),
I couldn't see an irq entry bind to uio driver under /proc/interrupts.
Am I doing anything wrong here?

Other method I have tried to get notified of the gpio pin0 interrupt in user space is to poll on /sys/class/gpio/gpio0/value. But merely exporting gpio0 
wasn't sufficient as kernel should make a call to request_irq on the gpio0 interrupt line. Is there a generic driver framework (like pinctrl) that can export
a device node to register the gpio pin0 as an interrupt source that allows me to poll on its sysfs entry?

All sysfs nodes can be polled as it is supported in kernel.
You can simply create a dummy driver and register the
irq and in your irq handler send udev notifications using
kobj.

Or
just update a sysfs node which can be polled from userspace.

If this answer is not sufficient then please explain in detail
what you are planning to achieve rather than what you are
doing to achieve that.

Thanks,
Rajasekhar

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