ESP32-C3 has a nice feature called GPIO Matrix which allows to map most of it's peripherals to any GPIO pin. And it has feature called IO_MUX which allows direct & faster operations for some of the high speed peripherals, including SPI. The API from ESP-IDF (HAL SDK) provides some library documentation on SPI functions.
But Arduino-ESP32 core documentation seems to completely miss SPI library & it's functions. It refers to basic Arduino SPI class, but it lacks description of features ESP32 family has.
I've found this example for ESP32 (note that I'm looking for ESP32-C3 info) which sets SPI pins through SPI.begin method actually.
I've also found this source which seems to feature a lot of SPI internal HAL functions. And a C++ SPI class sources are here. But it's actually doesn't have any useful comments on how to use IO_MUX or allowed values for ::setFrequency() method.
So basically I'm asking for a documentation on ESP32-C3 Arduino specific SPI class features. But to narrow things down I'm actually looking now how to initialize SPI2 (which is the only generally available SPI master on C3) as IO_MUX at the fastest SPI clock speed possible from the Arduino core/SPI class. Any suggestions are also welcomed!