Change the gpio_qdec driver to support optical encoders.
Add a property to use for defining an arbitrary number of GPIOs for the
sensing devices (typically infrared LEDs, but could also be the
biasing for the phototransistor), and one for adding a delay between
turning those on and reading the pin status.
The infrared LEDs typically consume a non negligible amount of power, so
there's also a new idle-poll-time-us property that enables two possible
modes of operation:
- if idle-poll-time-us is zero (default) the LEDs are enabled all the
time and the driver enters polling mode using the GPIO interrupt as
with mechanical encoders. This is usable for mains powered devices and
has the lowest overhead on the CPU.
- if idle-poll-time-us is non zero, then the driver polls the encoder
all the time, turning on the LEDs just before reading the state and
shutting them off immediately after, but when the encoder is idle it
switches the polling rate to idle-poll-time-us to save power, and only
polls at sample-time-us when some movement is detected.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
1dd2307b3f