USB CDC/ACM HOST CLASS DRIVER

```
Description: A CDC/ACM host class driver has been added. This has been
testing by running the USB CDC/ACM host on an Olimex
LPC1766STK and using the
boards/arm/stm32/stm3210e-eval/configs/usbserial
configuration (using the CDC/ACM device side driver). There
are several unresolved issues that prevent the host driver
from being usable:

- The driver works fine when configured for reduced or bulk-
only protocol on the Olimex LPC1766STK.

- Testing has not been performed with the interrupt IN channel
enabled (ie., I have not enabled FLOW control nor do I have
a test case that used the interrupt IN channel). I can see
that the polling for interrupt IN data is occurring
initially.

- I test for incoming data by doing 'nsh> cat /dev/ttyACM0' on
the Olimex LPC1766STK host. The bulk data reception still
works okay whether or not the interrupt IN channel is enabled.
If the interrupt IN channel is enabled, then polling of that
channel appears to stop when the bulk in channel becomes
active.

- The RX reception logic uses the low priority work queue.
However, that logic never returns and so blocks other use of
the work queue thread. This is probably okay but means that
the RX reception logic probably should be moved to its own
dedicated thread.

- I get crashes when I run with the STM32 OTGHS host driver.
Apparently the host driver is trashing memory on receipt
of data.

UPDATE: This behavior needs to be retested with:
commit ce2845c5c3c257d081f624857949a6afd4a4668a
Author: Janne Rosberg
Date: Tue Mar 7 06:58:32 2017 -0600

usbhost_cdcacm: fix tx outbuffer overflow and remove now
invalid assert

commit 3331e9c49aaaa6dcc3aefa6a9e2c80422ffedcd3
Author: Janne Rosberg
Date: Tue Mar 7 06:57:06 2017 -0600

STM32 OTGHS host: stm32_in_transfer() fails and returns NAK
if a short transfer is received. This causes problems from
class drivers like CDC/ACM where short packets are expected.
In those protocols, any transfer may be terminated by sending
short or NUL packet.

commit 0631c1aafa76dbaa41b4c37e18db98be47b60481
Author: Gregory Nutt
Date: Tue Mar 7 07:17:24 2017 -0600

STM32 OTGFS, STM32 L4 and F7: Adapt Janne Rosberg's patch to
STM32 OTGHS host to OTGFS host, and to similar implements for
L4 and F7.

- The SAMA5D EHCI and the LPC31 EHCI drivers both take semaphores
in the cancel method. The current CDC/ACM class driver calls
the cancel() method from an interrupt handler. This will
cause a crash. Those EHCI drivers should be redesigned to
permit cancellation from the interrupt level.

Most of these problems are unique to the Olimex LPC1766STK
DCD; some are probably design problems in the CDC/ACM host
driver. The bottom line is that the host CDC/ACM driver is
still immature and you could experience issues in some
configurations if you use it.

That all being said, I know of no issues with the current
CDC/ACM driver on the Olimex LPC1766STK platform if the interrupt
IN endpoint is not used, i.e., in "reduced" mode. The only loss
of functionality is output flow control.

UPDATE: The CDC/ACM class driver may also now be functional on
the STM32. That needs to be verified.

Status: Open
Priority: Medium-Low unless you really need host CDC/ACM support.
```

Start by reproducing the CDC/ACM host behavior with `nsh> cat /dev/ttyACM0` on the Olimex LPC1766STK using the `boards/arm/stm32/stm3210e-eval/configs/usbserial` configuration. Compare reduced and bulk-only protocol with interrupt IN enabled, then retest STM32 OTGHS after the commits listed in the issue. Done requires resolving the identified channel, work-queue, memory, and cancellation failures across the affected host configurations.

Written by the indexing model from the issue text.