Fix working with CDC-ACM (ttyACMx) / CH347T #229
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Currently, we have a serious problem with all CDC-ACM serial ports. For example, with the very popular USB-to-RS232 adapter CH347T:
We cannot set any modem control signals because the BRK signal is optional in CDC-ACM implementations.
See the Linux CDC-ACM driver source: https://github.com/torvalds/linux/blob/6fab32bb6508abbb8b7b1c5498e44f0c32320ed5/drivers/usb/class/cdc-acm.c#L930
A good solution is simply to ignore the ioctl error if it's EOPNOTSUPP.
Example: https://github.com/torvalds/linux/blob/2e590d67c2d803d603ac00b85f2fab235df52a1b/drivers/tty/tty_io.c#L2486