On Thu, Mar 20, 2014 at 02:31:30PM +0100, Martin Åkerberg wrote: > Hi Johan, > > You seem to be last contributor to cdc-acm driver in linux. I don't know if > you are the correct person to ask, or if you have the time to answer, but > if not, could you point me to the correct forum? The linux-usb list (added as CC) would be that forum. > Anyway, I am implementing a CDC-ACM device in a Atmel XMEGA processor. I am > interfacing this from a c-program on a Linux machine. Everything is working > as expected when it comes to opening the /dev/ttyACM0, configuring the > terminal, reading and sending data and closing the device. The problem > occurs when I try to open and close the device repeatedly many times. > > As a test: With a simple c-program I open and close the device in an > endless loop. Before every open and close I have a 100ms delay. I can see > on my device that setup messages with control line signals is sent on every > open and close, as expected. > > After about 50-500 cycles the open call fails. The message I can read in > dmesg is: > > [xxx] xhci_hcd 0000:00:14.0 ERROR no room on ep ring > [xxx] cdc_acm 3-3:1.1: acm_submit_read_urb - usb_submit_urb failed: -12 > > I read this as memory overflow regarding read urbs. I see in the kernel > code that 16 read urbs are allocated everytime the port is opened. But > these read urbs should be killed in the acm_port_shutdown function, which > might get called via > > tty_port_close > tty_port_shutdown > port->ops->shutdown > > I say "might" since it seems it doesn't happen in my case. > > Do you have any idea why this might be? Well, this appears to be a problem in the xhci-driver, and not directly related to cdc-acm. Specifically, the -ENOMEM (-12) above originates in the xhci-driver when it fails to enqueue the urb. [ The cdc-acm driver allocates its urbs on probe and releases them when the device is unbound. ] > I don't see any of the kernel warnings from tty_port_close_start, > > The "uname -r" output is: 3.2.0.23-generic That is a fairly old kernel (and also a distro-kernel?). I'd suggest you try to reproduce this on a more recent mainline kernel such as v3.13.6 (or v3.14-rc7). Thanks, Johan -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
