#spi_common.c

void spicommon_cs_initialize(spi_host_device_t host, int cs_io_num, int cs_num, int force_gpio_matrix)
{
    if (!force_gpio_matrix && cs_io_num == spi_periph_signal[host].spics0_iomux_pin && cs_num == 0) {
        //The cs0s for all SPI peripherals map to pin mux source 1, so we use that instead of a define.
        gpio_iomux_in(cs_io_num, spi_periph_signal[host].spics_in);
        gpio_iomux_out(cs_io_num, FUNC_SPI, false);
    } else {
        //Use GPIO matrix
        if (GPIO_IS_VALID_OUTPUT_GPIO(cs_io_num)) {
            gpio_set_direction(cs_io_num, GPIO_MODE_INPUT_OUTPUT_OD);
            gpio_matrix_out(cs_io_num, spi_periph_signal[host].spics_out[cs_num], false, false);
        } else {
            gpio_set_direction(cs_io_num, GPIO_MODE_INPUT);
        }
        if (cs_num == 0) gpio_matrix_in(cs_io_num, spi_periph_signal[host].spics_in, false);
        PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[cs_io_num], FUNC_GPIO);
    }
}