On Mon, Oct 25, 2010 at 12:24:23AM -0400, Debabrata Banerjee wrote:
> Hello all, this hang has been around for a long time, possibly more
> than 4 years, however probably due to timing changes I can hit this
> problem within minutes (vs days or weeks) on 2.6.35 (Ubuntu 10.10). So
> it's probably time to fix it. I'm mostly just poking around in the
> dark here as I've never looked at linux USB before.
Which 2.6.35.x stable kernel are you running? Can you reproduce it on
2.6.36?
> The hardware is hooked up as follows: IRTrans infrared
> receiver/display with an integrated FTDI usb-serial converter on
> board. To reproduce the hang the irserver daemon simply needs to be
> running while using the remote control (and producing data from the
> device). The daemon does a select() with a timeout of 10s on the USB
> device and then reads whatever bytes are present. In ftdi_sio.c this
> seems to cause ftdi_process_read_urb() to poll every 1 ms. Not what I
> expected but that's what is going on.
The driver uses a 1ms read timeout in order to reduce latencies. If this
is not a concern for you, you can increase the timeout (1..255ms) with
the following commands:
echo 128 > /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
You also need to clear the ASYNC_LOW_LATENCY flag for the port for the
change to take effect, e.g.:
setserial /dev/ttyUSB0 ^low_latency
/Johan
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