read USB bulk message on Linux - linux

Question

I am trying lessons on USB http://www.linuxforu.com/2011/12/data-transfers-to-from-usb-devices/ and stuck with the problem - while reading, usb_bulk_msg returns error 22 - Invalid argument. Write operation succeeds.
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/usb.h>
#define MIN(a,b) (((a) <= (b)) ? (a) : (b))
#define BULK_EP_OUT 0x01
#define BULK_EP_IN 0x82
#define MAX_PKT_SIZE 512
static struct usb_device *device;
static struct usb_class_driver class;
static unsigned char bulk_buf[MAX_PKT_SIZE];
static int pen_open(struct inode *i, struct file *f)
{
return 0;
}
static int pen_close(struct inode *i, struct file *f)
{
return 0;
}
static ssize_t pen_read(struct file *f, char __user *buf, size_t cnt, loff_t *off)
{
int retval;
int read_cnt;
/* Read the data from the bulk endpoint */
retval = usb_bulk_msg(device, usb_rcvbulkpipe(device, BULK_EP_IN),
bulk_buf, MAX_PKT_SIZE, &read_cnt, 5000);
if (retval)
{
printk(KERN_ERR "Bulk message returned %d\n", retval);
return retval;
}
if (copy_to_user(buf, bulk_buf, MIN(cnt, read_cnt)))
{
return -EFAULT;
}
return MIN(cnt, read_cnt);
}
static ssize_t pen_write(struct file *f, const char __user *buf, size_t cnt, loff_t *off)
{
int retval;
int wrote_cnt = MIN(cnt, MAX_PKT_SIZE);
if (copy_from_user(bulk_buf, buf, MIN(cnt, MAX_PKT_SIZE)))
{
return -EFAULT;
}
/* Write the data into the bulk endpoint */
retval = usb_bulk_msg(device, usb_sndbulkpipe(device, BULK_EP_OUT),
bulk_buf, MIN(cnt, MAX_PKT_SIZE), &wrote_cnt, 5000);
if (retval)
{
printk(KERN_ERR "Bulk message returned %d\n", retval);
return retval;
}
return wrote_cnt;
}
static struct file_operations fops =
{
.open = pen_open,
.release = pen_close,
.read = pen_read,
.write = pen_write,
};
static int pen_probe(struct usb_interface *interface, const struct usb_device_id *id)
{
int retval;
device = interface_to_usbdev(interface);
class.name = "usb/pen%d";
class.fops = &fops;
if ((retval = usb_register_dev(interface, &class)) < 0)
{
/* Something prevented us from registering this driver */
err("Not able to get a minor for this device.");
}
else
{
printk(KERN_INFO "Minor obtained: %d\n", interface->minor);
}
return retval;
}
static void pen_disconnect(struct usb_interface *interface)
{
usb_deregister_dev(interface, &class);
}
/* Table of devices that work with this driver */
static struct usb_device_id pen_table[] =
{
{ USB_DEVICE(0x058F, 0x6387) },
{} /* Terminating entry */
};
MODULE_DEVICE_TABLE (usb, pen_table);
static struct usb_driver pen_driver =
{
.name = "pen_driver",
.probe = pen_probe,
.disconnect = pen_disconnect,
.id_table = pen_table,
};
static int __init pen_init(void)
{
int result;
/* Register this driver with the USB subsystem */
if ((result = usb_register(&pen_driver)))
{
err("usb_register failed. Error number %d", result);
}
return result;
}
static void __exit pen_exit(void)
{
/* Deregister this driver with the USB subsystem */
usb_deregister(&pen_driver);
}
module_init(pen_init);
module_exit(pen_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anil Kumar Pugalia <email_at_sarika-pugs_dot_com>");
MODULE_DESCRIPTION("USB Pen Device Driver");

Answer 1

There could be many possible reasons for this error but in my case it happened that the BULK_EP address was wrong. I recommend setting up your endpoint addresses in the probe function rather than hard-coding them. Feel free to refer the below code to setup bulk endpoint addresses.
static void
set_bulk_address (
struct my_device *dev,
struct usb_interface *interface)
{
struct usb_endpoint_descriptor *endpoint;
struct usb_host_interface *iface_desc;
int i;
iface_desc = interface->cur_altsetting;
for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
endpoint = &iface_desc->endpoint[i].desc;
/* check for bulk endpoint */
if ((endpoint->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK)
== USB_ENDPOINT_XFER_BULK){
/* bulk in */
if(endpoint->bEndpointAddress & USB_DIR_IN) {
dev->bulk_in_add = endpoint->bEndpointAddress;
dev->bulk_in_size = endpoint->wMaxPacketSize;
dev->bulk_in_buffer = kmalloc(dev->bulk_in_size,
GFP_KERNEL);
if (!dev->bulk_in_buffer)
print("Could not allocate bulk buffer");
}
/* bulk out */
else
dev->bulk_out_add = endpoint->bEndpointAddress;
}
}
}
As you may notice, I have defined my own device struct to hold the endpoint information. Here is my struct definition
struct my_device {
struct usb_device *udev; /* usb device for this device */
struct usb_interface *interface; /* interface for this device */
unsigned char minor; /* minor value */
unsigned char * bulk_in_buffer; /* the buffer to in data */
size_t bulk_in_size; /* the size of the in buffer */
__u8 bulk_in_add; /* bulk in endpoint address */
__u8 bulk_out_add; /* bulk out endpoint address */
struct kref kref; /* module references counter */
};

Answer 2

The error is coming because you have to mention the correct bulk endpoints as per your usb device not the ones given in the example code.
For that you can either check /sys/kernel/debug/usb/devices file or /proc/bus/usb/devices.
In the file check the section containing your device's vendorId and productId and in that section check the E segment for endpoints.
In that segment the one with (I) will be BULK_EP_IN value and the one with (O) will be the value for BULK_EP_OUT.