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List:       linux-usb-users
Subject:    Re: [Linux-usb-users] turnering off USB devices
From:       Alan Stern <stern () rowland ! harvard ! edu>
Date:       2007-01-08 15:58:41
Message-ID: Pine.LNX.4.44L0.0701081051120.3804-100000 () iolanthe ! rowland ! org
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On 8 Jan 2007, Mattias Rönnblom wrote:

> Hi,
> 
> is there a way to turn off USB devices from user-space?

No.  However there is a way to suspend a USB device.  In order to use it, 
you must have a kernel with CONFIG_PM_SYSFS_DEPRECATED turned on.  To 
suspend a device, do (as root):

	echo -n 2 >/sys/bus/usb/devices/.../power/state

where the "..." is the ID for your device.  To unsuspend, do the same 
thing but with a "0" instead of the "2" above.

Note that this mechanism is slated to be removed from the kernel within 
the next year.  Hopefully some other mechanism will take its place.

> To reset a
> device?

Here's a program to do it.  You invoke it as either

	usbreset /proc/bus/usb/BBB/DDD
or
	usbreset /dev/usbB.D

depending on how your system is set up, where BBB and DDD are the bus and
device address numbers.

Alan Stern


-------------------

/* usbreset -- send a USB port reset to a USB device */

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>

#include <linux/usbdevice_fs.h>


int main(int argc, char **argv)
{
	const char *filename;
	int fd;
	int rc;

	if (argc != 2) {
		fprintf(stderr, "Usage: usbreset device-filename\n");
		return 1;
	}
	filename = argv[1];

	fd = open(filename, O_WRONLY);
	if (fd < 0) {
		perror("Error opening output file");
		return 1;
	}

	printf("Resetting USB device %s\n", filename);
	rc = ioctl(fd, USBDEVFS_RESET, 0);
	if (rc < 0) {
		perror("Error in ioctl");
		return 1;
	}
	printf("Reset successful\n");

	close(fd);
	return 0;
}


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