Hi all,
I am debugging an issue for a USB device (usb wifi dongle from TP-LINK
which is using Ralink chipset). I am using it on an embedded board
running Linux 2.6.30 on ARM architecture. The board has USB controller
from synopsys, and they've provided the driver for the same. The
controller has the feature to switch between USB speeds (i.e. 1.0 and
2.0). When I configure the USB controller in USB 1.0 speed, my USB
device (i.e. usb wifi dongle) works perfectly fine. But when the USB
controller is configured for USB 2.0, the device stops working after
some time when doing large data transfer at high speed. Its not crashing
the Linux, but the system becomes non-responsive. I could capture the
USB packets (using analyzer) between controller and device and found
that there was continuous PING - NAK token exchanges were happening. I
could re-confirm this scenario by putting some debug prints in
controller driver. From this observation, I assumed that it may happen
that device is not able to release the buffers and because of that its
sending NAK to each incoming PING request. When I reduced the number of
PINGs sent out by USB controller driver, the device was working fine.
Currently I am skipping every alternate PING token from controller driver.
I want to understand that what should be the ideal frequency to send
PING tokens. Should it be very aggressive? I searched through the code
of ehci driver in linux kernel, but could not figure out where the
exactly PING protocol is implemented in that. Can you please point out
the part of source code, so that I can look into it and see how it is
implemented ?
Thanks,
Vishal
--
To unsubscribe from this list: send an email with
"unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx
Please read the FAQ at http://kernelnewbies.org/FAQ
