2013/3/29 Sven Geggus <lists@fuchsschwanzdomain.de>
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 199 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L199>static struct gpio_keys_platform_data <http://lxr.linux.no/linux+v3.4.11/+code=gpio_keys_platform_data> baseboard_buttons_data <http://lxr.linux.no/linux+v3.4.11/+code=baseboard_buttons_data> = { 200 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L200> .buttons <http://lxr.linux.no/linux+v3.4.11/+code=buttons> = baseboard_buttons <http://lxr.linux.no/linux+v3.4.11/+code=baseboard_buttons>, 201 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L201> .nbuttons <http://lxr.linux.no/linux+v3.4.11/+code=nbuttons> = ARRAY_SIZE <http://lxr.linux.no/linux+v3.4.11/+code=ARRAY_SIZE>(baseboard_buttons <http://lxr.linux.no/linux+v3.4.11/+code=baseboard_buttons>), 202 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L202>}; 203 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L203> 204 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L204>static struct platform_device <http://lxr.linux.no/linux+v3.4.11/+code=platform_device> baseboard_buttons_device <http://lxr.linux.no/linux+v3.4.11/+code=baseboard_buttons_device> = { 205 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L205> .name <http://lxr.linux.no/linux+v3.4.11/+code=name> = "gpio-keys", 206 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L206> .id <http://lxr.linux.no/linux+v3.4.11/+code=id> = -1, 207 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L207> .dev <http://lxr.linux.no/linux+v3.4.11/+code=dev> = { 208 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L208> .platform_data <http://lxr.linux.no/linux+v3.4.11/+code=platform_data> = &baseboard_buttons_data <http://lxr.linux.no/linux+v3.4.11/+code=baseboard_buttons_data>, 209 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L209> }, 210 <http://lxr.linux.no/linux+v3.4.11/arch/sh/boards/mach-x3proto/setup.c#L210>};
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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