[libhid-discuss] HID Device hang

[Charles Lepple]

On Oct 16, 2007, at 8:23 AM, ankita prasad wrote:

> I am helping a professor who has written a very basic HID device  
> driver for
> his HID device. His code pretty much treats /dev/hiddev0 as a file  
> and uses
> ioctl calls  to to open a handle to the file and use it to read  
> from it and
> write to it.

The /dev/hiddev0 interface is the "kernel HID driver" that libhid  
detaches (the module is named "usbhid.ko", or "hid.ko" in earlier  
kernels).

> When using this driver, he can read and write to the device but  
> after about
> one minute, the device hangs. The only thing that I saw in his code  
> is that
> he doesn't explicitly blacklist the HID device from the kernel.  
> Could this
> be a reason for the sudden hang?

If you blacklist the HID device in the usbhid driver, you will  
prevent the system from creating the /dev/hiddev0 node when the  
device is plugged in. You would still be able to see the device with  
libhid, since it uses the core USB driver and usbdevfs, but there are  
no guarantees as to whether libhid will fare any better - often, when  
a USB device hangs, it is a problem with the device firmware.

-- 
Charles Lepple