Input device drivers test

There are three drivers example in this chapter. After running make command, there will be two modules:

input-button.ko
input-polled-button.ko
polled-ins.ko

The fist module implements the IRQ based input device, and the second one implements a polled input device. Both rely on i.MX6 from NXP. The third one should be used only on x86 platform, and will create a platform device that matches the polled input module.

The polled device can be partially tested on a PC. Prior to (partially) test this module on a PC, one should comment each line below in the code (input-polled-button.c):

    input_report_key(poll_dev->input, BTN_0, gpiod_get_value(priv->btn_gpiod) & 1);
    input_sync(poll_dev->input);
    gpiod_put(priv->btn_gpiod);

Polled input driver

On i.MX6 platforms, one can use the devicetree node below:

input_button_device {
    compatible = "packt,input-polled-button";
    button-gpios = <&gpio2 1 GPIO_ACTIVE_LOW>;
};

The module can then be loaded:

# insmod input-polled-button.ko

On x86 platform, one need to load polled-ins.ko too.

# insmod polled-ins.ko

after the module is loded, one can see the following debug message:

$ dmesg
[...]
[  335.044171] input-polled-button added
[  342.053497] input: Packt input polled Btn as /devices/platform/input-polled-button.0/input/input14

Now let's print some informations about the device using udevadm command:

$ udevadm info /dev/input/event14
P: /devices/platform/input-polled-button.0/input/input14/event14
N: input/event14
S: input/by-path/platform-input-polled-button.0-event
E: DEVLINKS=/dev/input/by-path/platform-input-polled-button.0-event
E: DEVNAME=/dev/input/event14
E: DEVPATH=/devices/platform/input-polled-button.0/input/input14/event14
E: ID_INPUT=1
E: ID_PATH=platform-input-polled-button.0
E: ID_PATH_TAG=platform-input-polled-button_0
E: MAJOR=13
E: MINOR=78
E: SUBSYSTEM=input
E: USEC_INITIALIZED=342093232

since the polled input driver can be partially tested on PC, the module loading may fail with below error in debug:

$ dmesg
[...]
[  277.561986] input_polled_button: Unknown symbol input_allocate_polled_device (err 0)
[  277.562012] input_polled_button: Unknown symbol input_free_polled_device (err 0)
[  277.562033] input_polled_button: Unknown symbol input_register_polled_device (err 0)
[  277.562050] input_polled_button: Unknown symbol input_unregister_polled_device (err 0)

This means our module tries to use non exported symbols. By using depmod, one can see our module dependencies, and load these prior to load our polled input module

$ modinfo ./input-polled-button.ko 
filename:       /home/ldd/sources/chapter-17/./input-polled-button.ko
description:    Polled input device
author:         John Madieu <john.madieu@gmail.com>
license:        GPL
srcversion:     9B24B13C64ECB6B10C912B3
depends:        input-polldev
vermagic:       4.4.0-97-generic SMP mod_unload modversions 

$ sudo modprobe  input-polldev

That is all for x86 based platform. Now on our i.MX6 based board, one can check the states of the gpio associated with this device as following:

# cat /sys/kernel/debug/gpio  | grep button
 gpio-193 (button-gpio         ) in  hi
# cat /sys/kernel/debug/gpio  | grep button
 gpio-193 (button-gpio         ) in  lo

One should run this command with the button pushed first, and then with the button released. The tool evtest cant be used to show the keycode corresponding to the button states:

# evtest /dev/input/event14 
Input driver version is 1.0.1
Input device ID: bus 0x0 vendor 0x0 product 0x0 version 0x0
Input device name: "Packt input polled Btn"
Supported events:
  Event type 0 (EV_SYN)
  Event type 1 (EV_KEY)
    Event code 256 (BTN_0)
Properties:
Testing ... (interrupt to exit)

IRQ based input driver

One can use the below node in the devicetree:

input_button_device {
    compatible = "packt,input-button";
    button-gpios = <&gpio2 1 GPIO_ACTIVE_LOW>;
};

You should make sure the GPIO is actually free. The command below will load the module:

# insmod input-polled-button.ko

using udevadm on the device will print the following informations:

# udevadm info /dev/input/event0 
P: /devices/platform/input-button.0/input/input0/event0
N: input/event0
S: input/by-path/platform-input-button.0-event
E: DEVLINKS=/dev/input/by-path/platform-input-button.0-event
E: DEVNAME=/dev/input/event0
E: DEVPATH=/devices/platform/input-button.0/input/input0/event0
E: ID_INPUT=1
E: ID_PATH=platform-input-button.0
E: ID_PATH_TAG=platform-input-button_0
E: MAJOR=13
E: MINOR=64
E: SUBSYSTEM=input
E: USEC_INITIALIZED=74842430

One can check whether the IRQ line has been acquired by the driver using the below command:

# cat /proc/interrupts
147:          0          0          0          0       GIC 147  20e0000.hdmi_video
150:        481          0          0          0       GIC 150  2188000.ethernet
151:          0          0          0          0       GIC 151  2188000.ethernet
152:         75          0          0          0       GIC 152  mx6-pcie-msi
160:          0          0          0          0  gpio-mxc   0  packt-input-button
161:          0          0          0          0  gpio-mxc   1  2198000.usdhc cd
250:          0          0          0          0  gpio-mxc  26  2-0026
286:          0          0          0          0  gpio-mxc  30  ad7606, ad7606, ad7606
351:          0          0          0          0  gpio-mxc  31  2-0027
352:          0          0          0          0  gpio-mxc   0  2194000.usdhc cd

the line with packt-input-button correspond to the IRQ line for this input device

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Input device drivers test

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Input device drivers test

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