I am trying to configure my Raspberry Zero W SPI interface to communicate lsb-first. I've modified spidev_test.c, but when I run it, I get an error:
uint8_t lsb_first = 1; ret = ioctl(fd, SPI_IOC_WR_LSB_FIRST, &lsb_first); if (ret == -1) pabort("can't set lsbfirst");
can't set lsbfirst: Invalid argument
If I set it to zero, it works.
Does the Raspberry Pi not support lsb-first? And if so, why is this apparently not documented anywhere?