USB Question about devices being reconnected to the host

From: Lucas Tanure <tanure@linux.com>
To: linux-usb@vger.kernel.org, kernelnewbies@kernelnewbies.org
Subject: USB Question about devices being reconnected to the host
Date: Thu, 15 Oct 2020 13:17:45 +0100	[thread overview]
Message-ID: <d4c94e87-a1bb-18d5-054f-2e6ed01fab5b@linux.com> (raw)

Hi,

I'm learning about USB drivers and I would like to know about 
disconnecting and reconnecting usb devices.

I can see my probe function being called and also the disconnect 
function. But if I reconnect the device there is no call from the kernel 
to notify my driver about the device being reconnected.

I can also see that the module for my driver was not unloaded, so I dont 
understand the life cycle of a USB device.

If the module is not unloaded at disconnection and re-loaded for a new 
device being connected, how can the driver know the device is there 
after a disconnection?

Thanks
Lucas

This is my dmesg for the driver at the end of this email:

[   34.706041] usb 1-1.1.2: new high-speed USB device number 5 using dwc_otg
[   34.837647] usb 1-1.1.2: New USB device found, idVendor=04b4, 
idProduct=00f1, bcdDevice= 0.00
[   34.837666] usb 1-1.1.2: New USB device strings: Mfr=1, Product=2, 
SerialNumber=0
[   34.837679] usb 1-1.1.2: Product: FX3
[   34.837693] usb 1-1.1.2: Manufacturer: Cypress
[   34.902480] usbdev_probe
[   34.902681] usbcore: registered new interface driver My USB Device
[   45.416310] usb 1-1.1.2: USB disconnect, device number 5
[   45.416655] usbdev_disconnect
[   61.326035] usb 1-1.1.2: new high-speed USB device number 6 using dwc_otg
[   61.457674] usb 1-1.1.2: New USB device found, idVendor=04b4, 
idProduct=00f1, bcdDevice= 0.00
[   61.457692] usb 1-1.1.2: New USB device strings: Mfr=1, Product=2, 
SerialNumber=0
[   61.457706] usb 1-1.1.2: Product: FX3
[   61.457720] usb 1-1.1.2: Manufacturer: Cypress

Driver:

#define DEBUG
#include <linux/of.h>
#include <linux/usb.h>
#include <linux/module.h>

static int usbdev_probe(struct usb_interface *intf, const struct 
usb_device_id *id)
{
	pr_info("%s", __func__);

	return 0;
}

static void usbdev_disconnect(struct usb_interface *intf)
{
	pr_info("%s", __func__);
}

static int usbdev_suspend(struct usb_interface *intf, pm_message_t message)
{
	pr_err("%s", __func__);
	return 0;
}

static int usbdev_resume(struct usb_interface *intf)
{
	pr_info("%s", __func__);
	return 0;
}

static int usbdev_reset_resume(struct usb_interface *intf)
{
	pr_info("%s", __func__);
	return 0;
}

static int usbdev_pre_reset(struct usb_interface *intf)
{
	pr_info("%s", __func__);
	return 0;
}

static int usbdev_post_reset(struct usb_interface *intf)
{
	pr_info("%s", __func__);
	return 0;
}

static const struct usb_device_id usbdev_id_table[] = {
	{ USB_DEVICE(0x04b4, 0x00f1) },
	{}
};
MODULE_DEVICE_TABLE(usb, usbdev_id_table);

static struct usb_driver usbdev_driver = {
	.name			= "My USB Device",
	.probe			= usbdev_probe,
	.disconnect		= usbdev_disconnect,
	.id_table		= usbdev_id_table,
	.suspend	 	= usbdev_suspend,
	.resume			= usbdev_resume,
	.reset_resume 	= usbdev_reset_resume,
	.pre_reset		= usbdev_pre_reset,
	.post_reset 	= usbdev_post_reset,
};

module_usb_driver(usbdev_driver);

MODULE_AUTHOR("Lucas Tanure <tanure@linux.com>");
MODULE_DESCRIPTION("Driver for My USB device");
MODULE_LICENSE("GPL v2");

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