USB request queuing?

From: Markus Grabner (grabner_at_icg.tu-graz.ac.at)
Date: 09/23/05 

Date: Fri, 23 Sep 2005 22:50:05 +0200

        Hi all!

    According to the documentation of the function "usb_submit_urb" in the
file "drivers/usb/core/urb.c", it is possible to submit URBs without having
to wait for completion of previous ones. It also says that as of Linux 2.6,
all queues have depth greater than one. However, when calling
usb_submit_urb five times in a driver I am developing (tested with Linux
versions 2.6.8, 2.6.11.5, and 2.6.13.2), I observe the following strange
behaviour:
1.) The device only responds to the first URB.
2.) The completion handler is only called for the first two URBs.
3.) The remaining completion handlers are called when unloading the driver
module (with urb->status == -ESHUTDOWN).
4.) After reloading the driver module, not a single completion handler is
called (only when unloading the driver - see above).
5.) To fix that, I have switch off and on the device or rmmod/insmod the
uhci_hcd module, then it starts again at 1.)

Is this a problem with the USB subsystem (do I have to set the queue depth
explicitly?), or does it simply mean that the device doesn't like to
receive USB data in quick succession?

Any hints are appreciated!

        Thanks & kind regards,
                Markus 

-- 
Markus Grabner - Computer Graphics and Vision
Graz University of Technology, Inffeldgasse 16/II, 8010 Graz, Austria
Phone: +43/316/873-5041, Fax: +43/316/873-5050
WWW: http://www.icg.tu-graz.ac.at/Members/grabner

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