via the new DIGIIO_SETALTPIN ioctl, and allow the port's ALTPIN setting
to be queried via DIGIIO_GETALTPIN.
The initial state and lock devices are normally used to set and/or
lock ALTPIN settings although the device itself may also be used.
ALTPIN settings are applied per-device and apply to both the callin
and callout device at the same time.
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