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GPIO API usage in Peripheral Drivers
When a peripheral driver initializes IOs, the general rule is to append necessary configurations onto the IO, instead of using any GPIO APIs that overwrite the current IO setting, such as gpio_config, gpio_set_direction, gpio_set_pull_mode.
Use gpio_pullup_en and gpio_pulldown_en to enable the internal pull-up/pull-down resistors if necessary.
Use gpio_od_enable to configure an output IO as open-drain mode if necessary.
Configure an IO as a peripheral signal output
There is no need to enable the output for the IO explicitly, it is done internally in the following function calls.
If the signal is routed through IO MUX to the pin, then only needs to call gpio_iomux_out to select the IO MUX function index.
If the signal is routed through GPIO Matrix to the pin, then first call gpio_func_sel to let the pin use PIN_FUNC_GPIO function, follow by calling esp_rom_gpio_connect_out_signal to connect the signal.
When a peripheral driver does de-initialization, to de-configure the pin as the peripheral signal output, a call to gpio_output_disable is enough. It will disconnect the signal internally.
Configure an IO as a peripheral signal input
If the signal is routed through IO MUX to the pin, then call gpio_iomux_out to select the IO MUX function index, and also call gpio_iomux_in to direct the signal to IO MUX. Input will be enabled for the IO internally.
If the signal is routed through GPIO Matrix to the pin, then first call gpio_func_sel to let the pin use PIN_FUNC_GPIO function, follow by calling gpio_input_enable and esp_rom_gpio_connect_in_signal to enable the input and connect the signal to the pin.
When a peripheral driver does de-initialization, to de-configure the pin as the peripheral signal input, use esp_rom_gpio_connect_in_signal to connect the signal to CONST_ONE or CONST_ZERO, so that it is disconnected from the pin. It is not desired to call gpio_input_disable, because there might be other drivers still using this pin as an input.