stm32 _hw_spi with libopencm3

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Hi, I have implemented u8x8_byte_stm32f4_hw_spi using the libopencm3 SPI calls. However, there may be a few wrinkles in my code as I am not an experienced C programmer. Also, as far as I can see, _hw_ calls are only inside the Arduino/CPP tree, am I right? Code is as follows:

#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/spi.h>
#include <libopencm3/stm32/gpio.h>

uint8_t u8x8_gpio_and_delay_stm32f4(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr);
uint8_t u8x8_byte_stm32f4_hw_spi(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr);

static void spi_setup(void) {
	rcc_periph_clock_enable(RCC_SPI2);
	rcc_periph_clock_enable(RCC_GPIOB);
	gpio_mode_setup(GPIOB, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO13|GPIO15 ); // SCK, MOSI - leaving out NSS
	gpio_set_output_options(GPIOB, GPIO_OTYPE_PP, GPIO_OSPEED_25MHZ, GPIO13|GPIO15);
	gpio_set_af(GPIOB, GPIO_AF5, GPIO13|GPIO15);
	gpio_mode_setup(GPIOB, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO12 ); // this is software driven NSS
	gpio_set_output_options(GPIOB, GPIO_OTYPE_PP, GPIO_OSPEED_25MHZ, GPIO12);
	gpio_set(GPIOB,GPIO12); // CS disable
	spi_reset(SPI2);
	spi_enable_software_slave_management(SPI2); // SPI hw not managing CS pin
	spi_set_nss_high(SPI2);
	spi_disable_ss_output(SPI2);
	spi_init_master(SPI2,SPI_CR1_BAUDRATE_FPCLK_DIV_8, SPI_CR1_CPOL_CLK_TO_0_WHEN_IDLE, SPI_CR1_CPHA_CLK_TRANSITION_1, SPI_CR1_DFF_8BIT, SPI_CR1_MSBFIRST); // unknown max clock speed, FPCLK_DIV_8 (about 2MHz?) seems to work
	spi_enable(SPI2);
	}

uint8_t u8x8_byte_stm32f4_hw_spi(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr) {
  static unsigned bitsleft;
  static uint8_t retaindata,datacommandbit;
  switch(msg)
  {
     case U8X8_MSG_BYTE_INIT:
       spi_setup();
       break;
     case U8X8_MSG_BYTE_SET_DC:
       datacommandbit=arg_int;
       break;
     case U8X8_MSG_BYTE_START_TRANSFER:
       if (u8x8->display_info->chip_enable_level) {
           gpio_set(GPIOB, GPIO12); // NSS: select SPI
         } else {
           gpio_clear(GPIOB,GPIO12);
         };
       bitsleft=0;
       break;
     case U8X8_MSG_BYTE_SEND: // implementing 9-bit-SPI, sending 8 bits, retaining 1 bit every cycle, until the 8th cycle
       for (int i=0; i<arg_int; i++) {
         uint8_t currentbyte,senddata;
         currentbyte=*(uint8_t *)(arg_ptr+i);
         senddata=(retaindata<<(8-bitsleft))|(datacommandbit << (7-bitsleft));
         retaindata=currentbyte;
         if (bitsleft < 7) senddata|=(currentbyte>>(bitsleft+1));
         spi_send(SPI2,senddata);
         bitsleft++;
         if (bitsleft==8) {
           spi_send(SPI2,retaindata);
           bitsleft=0;
         }
       }
       break;
     case U8X8_MSG_BYTE_END_TRANSFER:
       if (bitsleft) {
         spi_send(SPI2,retaindata<<(8-bitsleft));
         bitsleft=0;
       }
       while ((SPI_SR(SPI2) & SPI_SR_BSY)); // wait till all data is sent
       if (u8x8->display_info->chip_disable_level) {
           gpio_set(GPIOB, GPIO12); // NSS: select SPI
         } else {
           gpio_clear(GPIOB,GPIO12);
         };
       break;
     default:
       return 0;
   }
   return 1;
}

I implemented the u8x8_gpio_and_delay_stm32f4 with a stupid asm("nop"). (Yes and I know better). Also, a U8X8_MSG_GPIO_RESET was implemented, using port B bit 0.

So, does this code fit in u8g2 somewhere? If yes, how about the hardware choices? Using SPI2 instead of SPI1 is such a choice, also using GPIO12 for software CS and GPIO0 for reset is arbitrary. I'm not sure how to make this flexible - probably with some preprocessor wizardry? I'll be happy to make the above code a pull request if anyone can tell me where it would fit.