This patch equips the pin-driver framework with support for the
time-multiplexed operation of a pin as output or input. This is needed
when implementing I2C communication via a bit-banging driver.
To operate pin in both directions, a driver obtains both a pin-state and
a pin-control session for the same pin. The pin-state session can be
used to sense the current pin state. The control session allows the
client to set the pin to high or low (using the 'state' method), or to
set it to high-impedance via the 'yield' method. Once switched to
high-impedance, the pin can be used as input.
Issue genodelabs/genode-allwinner#10
The new interfaces are meant to gradually replace the existing
Gpio_session interface.
- Each session refers to a single pin.
- The session types distiguish the direction of the signal as input or
output.
- Pin coordinates can be selected via session labels.
- GPIO interrupts are covered by the regular IRQ session interface.
The interfaces are accompanied by framework utilities and interfaces:
- os/pin_driver.h
- pin_control_session/component.h
- pin_state_session/component.h
These headers relieve GPIO drivers from implementing boilerplate code by
providing device-agnostic portions. The A64 pio driver serves as
reference for using those utilities.
https://github.com/nfeske/genode-allwinner/tree/master/src/drivers/pin/a64Fixes#4315
