Linux Driver Programming: Problem with usb_control_msg - c

Question

Short Version
I want to write a Linux Driver for a custom USB device. Before writing the driver I used libusb-1.0 to test the device. With the following function call, I could read out a uin16_t value from the device:
status = libusb_control_transfer(handle, /* Device Handle */
0x80, /* bRequestType */
0x10, /* bRequest */
value, /* wValue */
0x0, /* wIndex */
((uint8_t *) &value), /* data */
2, /* wLength */
100); /* timeout */
After this call, I got a new value in the value variable.
Now I want to accomplish the same call in my Driver. I have tried the following in the probe function of my USB driver:
status = usb_control_msg(data->udev, usb_rcvctrlpipe(data->udev, 0), 0x10, USB_DIR_IN, 0, 0, (u8*) &my_data, 2, 100);
All I get is the return value -11 and on my device I don't see anything.
The only thing I am doing before this call, is calling data->udev = interface_to_usbdev(intf); to get the USB device from my interface.
Does anyone know, if I am missing something or if I am doing something wrong?
Long version
I want to learn how to write USB Drivers in Linux. As a DUT for which I can write a driver, I choose a Raspberry Pi Pico and the dev_lowlevel USB example. I adapt the code a little bit, so I can use a control transfer with bRequest 0x10 and bRequestType 0x0 (USB_DIR_OUT) to turn the Pico's onboard LED on or off and a control transfer with bRequest 0x10 and bRequestType 0x80 (USB_DIR_IN) to read back the current value of the LED.
With a user space program and the following code I can read out the value of the LED and turn it on or off:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <libusb-1.0/libusb.h>
#define VID 0x0000
#define DID 0x0001
int main(int argc, char **argv) {
int status, len;
libusb_device_handle *handle = NULL;
/* Init Libusb */
status = libusb_init(NULL);
if(status < 0) {
printf("Error init USB!\n");
return status;
}
handle = libusb_open_device_with_vid_pid(NULL, VID, DID);
if(!handle) {
printf("No device found with %04x:%04x\n", VID, DID);
libusb_exit(NULL);
return -1;
}
if(argc > 1)
value = atoi(argv[1]);
else {
/* Do control transfer */
status = libusb_control_transfer(handle, /* Device Handle */
0x80, /* bRequestType */
0x10, /* bRequest */
value, /* wValue */
0x0, /* wIndex */
((uint8_t *) &value), /* data */
2, /* wLength */
100); /* timeout */
if(status < 0) {
printf("Error during control transfer!\n");
libusb_close(handle);
libusb_exit(NULL);
return -1;
}
printf("Got: %d\n", value);
value = (value + 1) & 0x1;
}
/* Do control transfer */
status = libusb_control_transfer(handle, 0x0, 0x10, value, 0x0, NULL, 0, 100);
if(status < 0) {
printf("Error during control transfer!\n");
libusb_close(handle);
libusb_exit(NULL);
return -1;
}
libusb_close(handle);
libusb_exit(NULL);
return 0;
}
Now I want to control my device over a USB Driver. Here is what I got already:
#include <linux/module.h>
#include <linux/init.h>
#include <linux/usb.h>
#include <linux/slab.h>
/* Meta Information */
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Johannes 4 GNU/Linux");
MODULE_DESCRIPTION("Driver for my custom RPi Pico USB device");
struct pico_usb {
struct usb_device *udev;
};
#define PICO_VID 0x0000
#define PICO_PID 0x0001
static struct usb_device_id pico_usb_table [] = {
{ USB_DEVICE(PICO_VID, PICO_PID) },
{},
};
MODULE_DEVICE_TABLE(usb, pico_usb_table);
static int pico_usb_probe(struct usb_interface *intf, const struct usb_device_id *id) {
struct pico_usb *data;
int status;
int my_data;
printk("pico_usb_drv - Now I am in the Probe function!\n");
data = kzalloc(sizeof(struct pico_usb), GFP_KERNEL);
if(!data) {
printk("pico_usb_drv - Out of memory\n");
return -ENOMEM;
}
data->udev = interface_to_usbdev(intf);
usb_set_intfdata(intf, data);
/* Turn the LED on */
status = usb_control_msg(data->udev, usb_sndctrlpipe(data->udev, 0), 0x10, USB_DIR_OUT, 1, 0, 0, 0, 100);
/* Read LED state */
printk("pico_usb_drv - status USB_DIR_OUT: %d\n", status);
status = usb_control_msg(data->udev, usb_rcvctrlpipe(data->udev, 0), 0x10, USB_DIR_IN, 0, 0, (u8*) &my_data, 2, 100);
printk("pico_usb_drv - status USB_DIR_IN: %d\n", status);
return 0;
}
static void pico_usb_disconnect(struct usb_interface *intf) {
struct pico_usb *data;
printk("pico_usb_drv - Now I am in the Disconnect function!\n");
data = usb_get_intfdata(intf);
kfree(data);
}
static struct usb_driver pico_usb_driver = {
//.owner = THIS_MODULE,
.name = "pico_usb",
.id_table = pico_usb_table,
.probe = pico_usb_probe,
.disconnect = pico_usb_disconnect,
};
/**
* #brief This function is called, when the module is loaded into the kernel
*/
static int __init pico_usb_init(void) {
int result;
printk("pico_usb_drv - Registering the PICO USB device\n");
result = usb_register(&pico_usb_driver);
if(result) {
printk("pico_usb_drv - Error registering the PICO USB device\n");
return -result;
}
return 0;
}
/**
* #brief This function is called, when the module is removed from the kernel
*/
static void __exit pcio_usb_exit(void) {
printk("pico_usb_drv - Unregistering the PICO USB device\n");
usb_deregister(&pico_usb_driver);
}
module_init(pico_usb_init);
module_exit(pcio_usb_exit);
The first control message works and my LED is turned on. But the second control message doesn't do anything, but gives me the error code -11 back.
Does anyone know, if I am missing something or if I am doing something wrong?

Answer 1

Ok, I found the solution. Instead of usb_control_msg I use usb_control_msg_recv now and everything works just fine.
usb_control_msg_recv takes one more argument:
int usb_control_msg_recv(struct usb_device *dev, __u8 endpoint, __u8 request, __u8 requesttype, __u16 value, __u16 index, void *driver_data, __u16 size, int timeout, gfp_t memflags)
As I pass the pointer to a variable and don't want to allocate memory dynamically, I set the memflags argument to 0.