Re: Failing USB_XFER_LOCK_ASSERT condition

> Hi all,
>
> I am trying to submit a usbd_transfer_start, but hitting the assertion 
> error here:
> http://bxr.su/FreeBSD/sys/dev/usb/usb_transfer.c#1954, which is this 
> line:
> USB_XFER_LOCK_ASSERT(xfer, MA_OWNED);
>
> I noticed that when I lock the device with mtx_lock(sc->sc_mtx) I do 
> not hit that assertion condition but I do without it. However, looking 
> at other device drivers, they do not need an explicit 
> DEVICE_LOCK/UNLOCK around each transfer.
>
> What is the common pattern that would prevent this? I am probably 
> missing something, but am unclear on what.
> Thank you,

I figured it out...I completely misunderstood how a mutex worked in relation to a USB transfer. In short, the usdb_transfer_start requires the mutex to be locked that was created during the usbd_transfer_setup.

Hope that helps someone in the future.