Regardless of direction, a write to GPIO data actually succeeds fully with all 4 bits. However, this does not directly touch the pin state. It instead places it into an internal write only latch. This latch asserts bits onto the pin state if direction allows for such, otherwise the other side (e.g. RTC) will be the one asserting bits (but this does not end up touching the internal write latch).
The implementation here is likely not entirely accurate for direction changes from out to in (as that depends on each external device implementation), but it should be correct for in to out changes.
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