Attaching device with device driver - linux

Question

I am trying to learn about Linux platform drivers. I have taken a driver from the following tutorial:
http://linuxseekernel.blogspot.com/2014/05/platform-device-driver-practical.html
It is a basic platform driver. I have compiled it and loaded the module. It loads fine, however, its probe function is never executed. There is a lot of documentation that has said as long as the devices id and drivers id match, then the probe function is called. Well I have the following driver:
#include <linux/module.h>
#include <linux/kernel.h>
//for platform drivers....
#include <linux/platform_device.h>
#define DRIVER_NAME "twl12xx"
MODULE_LICENSE("GPL");
/**************/
static int sample_drv_probe(struct platform_device *pdev){
printk(KERN_ALERT "twl12xx: Probed\n");
return 0;
}
static int sample_drv_remove(struct platform_device *pdev){
printk(KERN_ALERT "twl12xx: Removing twl12xx\n");
return 0;
}
static const struct platform_device_id twl12xx_id_table[] = {
{ "twl12xx", 0},
{}
};
MODULE_DEVICE_TABLE(platform, twl12xx_id_table);
static struct platform_driver sample_pldriver = {
.probe = sample_drv_probe,
.remove = sample_drv_remove,
.driver = {
.name = DRIVER_NAME,
},
};
/**************/
int ourinitmodule(void)
{
printk(KERN_ALERT "\n Welcome to twl12xx driver.... \n");
/* Registering with Kernel */
platform_driver_register(&sample_pldriver);
return 0;
}
void ourcleanupmodule(void)
{
printk(KERN_ALERT "\n Thanks....Exiting twl12xx driver... \n");
/* Unregistering from Kernel */
platform_driver_unregister(&sample_pldriver);
return;
}
module_init(ourinitmodule);
module_exit(ourcleanupmodule);
I also have the following entry in my device tree:
twl12xx: twl12xx#2 {
compatible = "twl12xx";
};
I feel like I am must be missing something or incorrectly defining my device tree.

Answer 1

Whatever you have read is correct; driver and device ID both should match.
You have just create the skeleton of driver and you are using the device tree. So it looks fine. But you are missing the of_match_table entry in your code; which is very important for device ID match (same string as you have pass from the device tree) and driver probe calling.
So add the below changes your code:
#ifdef CONFIG_OF
static const struct of_device_id twl12xx_dt_ids[] = {
.compatible = "ti,twl12xx",
{}
};
MODULE_DEVICE_TABLE(of, twl12xx_dt_ids);
#endif
static struct platform_driver sample_pldriver = {
.probe = sample_drv_probe,
.remove = sample_drv_remove,
.driver = {
.name = DRIVER_NAME,
.of_match_table = of_match_ptr(twl12xx_dt_ids),
},
.id_table = twl12xx_id_table,
};

Answer 2

I had similar problem. Probe function also wasn't able to print anything. The reason in my case was: In my linux I had ready driver that was binded to the device . When I unbinded this driver, Probe function worked successfully.
(Note, to unbind:
cd /sys/bus/platform/drivers/<driver_name>
echo "device_name" > unbind
)