Re: How is gpio_keys.ko supposed to work?

[Jerry Zhang <jerry.scofield@xxxxxxxxx>]

2013/3/29 Sven Geggus <lists@xxxxxxxxxxxxxxxxxxxxx>

Hello,

I have a userland application on Raspberry Pi which uses select to read
input from a button connected to gpio like this:

GPIO --+---- BUTTON ----- GND
       |
       +--- RESISTOR 2k -- VCC (3.3V)

The sysfs "file" I use select at is /sys/class/gpio/gpioX/value with the
method found in Documentation/gpio.txt.

However, this same file also states the following:
Note that standard kernel drivers exist for common "LEDs and Buttons"
GPIO tasks:  "leds-gpio" and "gpio_keys", respectively.  Use those
instead of talking directly to the GPIOs; they integrate with kernel
frameworks better than your userspace code could.

So how can I make this "standard kernel drivers" work?

I would like to get rid of using /sys/class/gpio/gpioX/value and use
/dev/input/eventX instead, because the first method will require debouncing
in userland and is not portable to other keyboard types.

I tried to compile a kernel with CONFIG_KEYBOARD_GPIO enabled and load
gpio_keys.ko. However this did neither create a new device in /dev/input/
nor /sys/devices/platform/gpio-keys.

The entry will only be created after the "Driver" probes the "Device" successfully. In your case, you need to be sure the corresponding platform_device is claimed in your board setup code. The setup logic vary from Arch/mach to Arch/mach. Here is one example from sh.

http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c

static struct gpio_keys_platform_data baseboard_buttons_data = {
        .buttons        = baseboard_buttons,
        .nbuttons       = ARRAY_SIZE(baseboard_buttons),
};

static struct platform_device baseboard_buttons_device = {
        .name           = "gpio-keys",
        .id             = -1,
        .dev            = {
                .platform_data  = &baseboard_buttons_data,
        },
};

 

Kconfig states the following:
...
Your board-specific setup logic must also provide a platform device,
with configuration data saying which GPIOs are used.
...

So looks like my "board-specific setup logic" (whatever this might be) does
not "provide a platform device with configuration data saying which GPIOs
are used".

So my question is twofold:
1. Where can I find the "board-specific setup logic" (for Rapberry Pi in my
case
2. How would this "board-specific setup logic" (if unavailable) look like to
make gpio_keys.ko work?

Sven

P.S.: The kernel in use is the one from
git://github.com/raspberrypi/linux.git which is basically a vanilla 3.6.11
with Raspberry Pi specific patches.

--
Threading is a performance hack.
(The Art of Unix Programming by Eric S. Raymond)

/me is giggls@ircnet, http://sven.gegg.us/ on the Web

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