user button from driver

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1

Hello to all,
I'm writing a device driver for beagle, and I want to control the
on-board user button (GPIO_7) in order to register an interrupt from
this button. In other words, I simply want the button to be associated
with an interrupt handler I wrote.
I'm trying to use the kernel GPIO API, but the gpio_request() call
returns with -EBUSY. Then, while gpio_to_irq() correctly returns the
irq number (as I can see it in /proc/interrupts), request_irq()
returns -EBUSY again.
The call sequence is

...
gpio_request(GPIO_7, "gpio");
irq = gpio_to_irq(GPIO_7);
request_irq(irq, my_handler, IRQF_SHARED, name, NULL);
...

How can I free such irq in order to manage it?

Thanks

Daniele

2

I’m purely guessing here, but the fact that the normal kernel configuration sets up that button with an internal interrupt handler and then enables a keyboard like event would seem to mean that you need to modify your kernel build to disable the default operation of that button.

Wim.

3

Googling i'm finding many drivers that use omap-specific functions,
such as omap_request_gpio() or something like that. I found
declarations of such functions in the arch/arm/plat-omap/include/*
directory.
But i'm new to kernel development, and i can't figure out how to
include files from that dir...
Maybe calling omap functions is needed in order to request gpio lines,
is it correct?
Sorry for the newbie questions...

Daniele

4

I’m pretty sure that USER-button is already acquired by kernel. Just find the place in kernel and disable it.

2010/11/22 Daniele Capuano <el.einad@gmail.com>

5

Daniele - sorry I don’t have any direct advice, but here is an excellent resource for Linux device drivers:

http://lwn.net/Kernel/LDD3/

6

Do you think that I have to disable ALL the GPIO support in kernel
configuration? It seems to be quite a dramatic solution...but i can't
find where is any gpio-specific driver in kernel...
please help...!

Daniele

p.s. @Jeff Yes, that is my reference book for deleloping my
driver...but gpio is not taken into account...

7

You need to learn how to find necessary code in the kernel source, because the kernel itself is the perfect book about linux device drivers :slight_smile:

Try to use “grep” utility to search for text. For instance something like:

grep GPIO * -r | grep omap

2010/11/23 Daniele Capuano <el.einad@gmail.com>

8

Daniele,

Take a look at this gentleman's page, he does almost exactly what
you're looking to do, and provides ample code examples to accomplish
the task.

http://wh1t3s.com/tag/beagleboard/

Good luck!

9

Have a look into the kernel source:

Documentation/gpio.txt explains the way GPIO are managed by the kernel. Note the user interface through sysfs.

arch/arm/plat-omap/gpio.c is the platform code used by the generic gpio framework.

Have fun !

10

I found the kernel configuration at
"Device Drivers -> Input Device Support-> Keyboards - > GPIO Buttons"
that seems to perfectly match the case. Now, since this is a built-in
configuration and cannot be disabled without recompiling, i'm going to
recompile and retry...
Thanks a lot!

Daniele

11

Can’t we configure the gpio_keys driver to call my custom ISR for user button? If not, then as discussed in this thread we need to disable GPIO buttons from menu config and write a module where we can request for user button and register it with custom handler?

Thanks
Sanket