In the failure case, does the system literally have no serial ports left (ie: is userspace incorrectly sending syscalls wildly into the ether without checking), or is it that you're shuffling port assignments by adding/removing ports, and we're now trying to configure a *different* driver that doesn't take kindly to the old config?
In the failure case, does the system literally have no serial ports left (ie: is userspace incorrectly sending syscalls wildly into the ether without checking), or is it that you're shuffling port assignments by adding/removing ports, and we're now trying to configure a *different* driver that doesn't take kindly to the old config?