spi_max_transfer_size
size_t max_size = spi_max_transfer_size(spi);
size_t max_chunk = spi_max_transfer_size(spi);
max_size = spi_max_transfer_size(spi);
max_xfer = spi_max_transfer_size(spi);
if (len > spi_max_transfer_size(mem->spi))
spi_max_transfer_size(mem->spi),
spi_max_transfer_size(msg->spi));