I need to change mux from GPIO to SPI at runtime, only when I need to use SPI at certain condition.
Since I do not have enough GPIO, I want to reuse SPI interface with GPIO(LED output).
SPI_MOSI and SPI_CLK as LED output and SPI_CS as LED enable.
mux is set to GPIO at init.
when I need to use SPI, I set mux as SPI.
when SPI_CS is active, LED output will be disabled.
