Re: USB Gadget Serial Blocking Read Problem

On Friday 13 July 2007, Sagusti.Robert wrote:
> Hi,
> 
> I'm running kernel 2.6.20 on an AT91RM9200 processor. I have
> the gadget serial driver loaded and I am successfully reading
> and writing data in and out the USB port to a windows terminal.
> In my user code, when I open the gadget driver port, I open it
> with the default blocking flag so that my user thread will
> sleep while waiting for data to come in. My problem is that
> when I pull the USB cable which causes a disconnect, the read()
> call never returns in my user code thereby locking the thread
> that it is called in.        

Looks like gs_free_ports() only updates the write side,
not the read side ...


> I have turned on debugs in the driver's module and am I am
> monitoring the Gadget Driver in another thread by cat /proc/kmsg
> and can clearly see that the Gadget Driver function
> gs_disconnect(struct usb_gadget *gadget) is being called. The
> driver reacts fine to the connects and disconnects but the user
> mode read() function is the problem. I'm pretty new to driver
> development and I've been attempting to trace the problem
> through the tty driver and the line discipline to attempt
> to understand how things work. After 3 days, I'm gaining some
> understanding but I really could use some help.         
> 
> I would think that lots of apps would have to handle the USB
> cord being yanked out. Does anyone have any insight into this?  

Just that this is clearly a bug in the serial gadget code.

The way gadget drivers are supposed to handle disconnect
events is to (cleanly) shut down all pending I/O ... and
it's not doing that except for write operations.

- Dave

 
> Thanks for reading.
> 
> 
> 
> 
> Robert P. Sagusti
> ENSCO Inc., APA Division
> 5400 Port Royal Rd.
> Springfield, VA  22151
> (703) 321-4407
> [email protected]
> 




-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/
_______________________________________________
[email protected]
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-devel