Help on modelling gpio interrupt source when interrupt is shared

[Anish Kumar]

> On Jan 23, 2017, at 10:56 PM, Rajasekhar Pulluru <pullururajasekhar at gmail.com> wrote:
> 
> Hi Anish,
> 
> My intention is just to detect interrupt in the user space and read the device id without using udev.
> 
> I don't want to create a new driver in kernel (assume I can't modify linux kernel sources), which is the first reason to go for uio generic platform driver.
> 
> If I register a gpio interrupt (level triggered) using a kernel module, I can get the interrupt detected

Which means you are able to do insmod, so you can very well write a kernel module and send some event to user space.
> when device is inserted/removed. But I would like to detect device presence completely from user space without modifying linux kernel.
> 
> Thanks & Regards,
> Rajasekhar
> 
>> On Tue, Jan 24, 2017 at 11:56 AM, anish singh <anish198519851985 at gmail.com> wrote:
>> 
>> 
>>> On Mon, Jan 23, 2017 at 7:46 AM, Rajasekhar Pulluru <pullururajasekhar at 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 at 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 at 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.
>>  
>>> tree configuration. (following https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/)
>>> 
>>>         user_io at 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
>>> 
>>> _______________________________________________
>>> Kernelnewbies mailing list
>>> Kernelnewbies at kernelnewbies.org
>>> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>> 
>> 
> 
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