Как заставить работать SD в режиме mmc-spi на процессоре Altera NIOS2 под управением Linux?

int mmc_wait_for_app_cmd(struct mmc_host *host, struct mmc_card *card,
	struct mmc_command *cmd, int retries)
{
	struct mmc_request mrq = {NULL};

	int i, err;

	BUG_ON(!cmd);
	BUG_ON(retries < 0);

	err = -EIO;

	/*
	 * We have to resend MMC_APP_CMD for each attempt so
	 * we cannot use the retries field in mmc_command.
	 */
	for (i = 0;i <= retries;i++) {
		err = mmc_app_cmd(host, card);
		if (err) {
			/* no point in retrying; no APP commands allowed */
			if (mmc_host_is_spi(host)) {
				if (cmd->resp[0] & R1_SPI_ILLEGAL_COMMAND)
					break;
			}
			continue;
		}

		memset(&mrq, 0, sizeof(struct mmc_request));

		memset(cmd->resp, 0, sizeof(cmd->resp));
		cmd->retries = 0;

		mrq.cmd = cmd;
		cmd->data = NULL;

		mmc_wait_for_req(host, &mrq);

		err = cmd->error;
		if (!cmd->error)
			break;

		/* no point in retrying illegal APP commands */
		if (mmc_host_is_spi(host)) {
			if (cmd->resp[0] & R1_SPI_ILLEGAL_COMMAND)
				break;
		}
	}

	return err;
}