refactor(gpio): public some IO configuration functions

This allows different peripheral drivers to act on the same IO.

docs/en/api-reference/peripherals/gpio.rst

@@ -29,6 +29,18 @@ GPIO Summary
         - Analog functions such as ADC/DAC/etc are in use
         :SOC_LP_PERIPHERALS_SUPPORTED: - LP peripherals, such as LP_UART, LP_I2C, are in use
 
+IO Configuration
+----------------
+
+An IO can be used in two ways:
+
+- As a simple GPIO input to read the level on the pin, or as a simple GPIO output to output the desired level on the pin.
+- As a peripheral signal input/output.
+
+IDF peripheral drivers always take care of the necessary IO configurations that need to be applied onto the pins, so that they can be used as the peripheral signal inputs or outputs. This means the users usually only need to be responsible for configuring the IOs as simple inputs or outputs. :cpp:func:`gpio_config` is an all-in-one API that can be used to configure the I/O mode, internal pull-up/pull-down resistors, etc. for pins.
+
+In some applications, an IO pin can serve dual purposes. For example, the IO, which outputs a LEDC PWM signal, can also act as a GPIO input to generate interrupts or GPIO ETM events. Careful handling on the configuration step is necessary for such dual use of IO pins cases. :cpp:func:`gpio_config` is an API that overwrites all the current configurations, so it must be called to set the pin mode to :cpp:enumerator:`gpio_mode_t::GPIO_MODE_INPUT` before calling the LEDC driver API which connects the output signal to the pin. As an alternative, if no other configuration is needed other than making the pin input enabled, :cpp:func:`gpio_input_enable` can be the one to call at any time to achieve the same purpose.
+
 Check Current Configuration of IOs
 ----------------------------------
 
@@ -75,7 +87,7 @@ If an IO pin is routed to a peripheral signal through the GPIO matrix, the signa
 
 Do not rely on the default configurations values in the Technical Reference Manual, because it may be changed in the bootloader or application startup code before app_main.
 
-.. only:: esp32c3 or esp32c6 or esp32h2 or esp32p4 or esp32s2 or esp32s3 or esp32c5
+.. only:: esp32c3 or esp32c6 or esp32h2 or esp32p4 or esp32s2 or esp32s3 or esp32c5 or esp32c61
 
     Configure USB PHY Pins to GPIO
     -------------------------------

docs/en/api-reference/peripherals/pcnt.rst

@@ -87,7 +87,6 @@ To install a PCNT channel, you must initialize a :cpp:type:`pcnt_chan_config_t`
 - :cpp:member:`pcnt_chan_config_t::edge_gpio_num` and :cpp:member:`pcnt_chan_config_t::level_gpio_num` specify the GPIO numbers used by **edge** type signal and **level** type signal. Please note, either of them can be assigned to ``-1`` if it is not actually used, and thus it will become a **virtual IO**. For some simple pulse counting applications where one of the level/edge signals is fixed (i.e., never changes), you can reclaim a GPIO by setting the signal as a virtual IO on channel allocation. Setting the level/edge signal as a virtual IO causes that signal to be internally routed to a fixed High/Low logic level, thus allowing you to save a GPIO for other purposes.
 - :cpp:member:`pcnt_chan_config_t::virt_edge_io_level` and :cpp:member:`pcnt_chan_config_t::virt_level_io_level` specify the virtual IO level for **edge** and **level** input signal, to ensure a deterministic state for such control signal. Please note, they are only valid when either :cpp:member:`pcnt_chan_config_t::edge_gpio_num` or :cpp:member:`pcnt_chan_config_t::level_gpio_num` is assigned to ``-1``.
 - :cpp:member:`pcnt_chan_config_t::invert_edge_input` and :cpp:member:`pcnt_chan_config_t::invert_level_input` are used to decide whether to invert the input signals before they going into PCNT hardware. The invert is done by GPIO matrix instead of PCNT hardware.
-- :cpp:member:`pcnt_chan_config_t::io_loop_back` is for debug only, which enables both the GPIO's input and output paths. This can help to simulate the pulse signals by function :cpp:func:`gpio_set_level` on the same GPIO.
 
 Channel allocating and initialization is done by calling a function :cpp:func:`pcnt_new_channel` with the above :cpp:type:`pcnt_chan_config_t` as an input parameter plus a PCNT unit handle returned from :cpp:func:`pcnt_new_unit`. This function will return a PCNT channel handle if it runs correctly. Specifically, when there are no more free PCNT channel within the unit (i.e., channel resources have been used up), then this function will return :c:macro:`ESP_ERR_NOT_FOUND` error. The total number of available PCNT channels within the unit is recorded by :c:macro:`SOC_PCNT_CHANNELS_PER_UNIT` for reference. Note that, when install a PCNT channel for a specific unit, one should ensure the unit is in the init state, otherwise this function will return :c:macro:`ESP_ERR_INVALID_STATE` error.
 
@@ -247,7 +246,6 @@ This function should be called when the unit is in the init state. Otherwise, it
 
         -  :cpp:member:`pcnt_clear_signal_config_t::clear_signal_gpio_num` specify the GPIO numbers used by **clear** signal. The default active level is high, and the input mode is pull-down enabled.
         -  :cpp:member:`pcnt_clear_signal_config_t::invert_clear_signal` is used to decide whether to invert the input signal before it going into PCNT hardware. The invert is done by GPIO matrix instead of PCNT hardware. The input mode is pull-up enabled when the input signal is inverted.
-        -  :cpp:member:`pcnt_clear_signal_config_t::io_loop_back` is for debug only, which enables both the GPIO's input and output paths. This can help to simulate the clear signal by function :cpp:func:`gpio_set_level` for the same GPIO.
 
     This signal acts in the same way as calling :cpp:func:`pcnt_unit_clear_count`, but is not subject to software latency, and is suitable for use in situations with low latency requirements. Also please note, the flip frequency of this signal can not be too high.