"If /dev/mdev.seq file exists, mdev will wait for its value
to match $SEQNUM variable. This prevents plug/unplug races.
To activate this feature, create empty /dev/mdev.seq at boot."

So create empty /dev/mdev.seq ... but the code expects the file to contain new line

        if (seqbuf[0] == '\n') {
            /* seed file: write out seq ASAP */
            xwrite_str(seq_fd, seq);
            xlseek(seq_fd, 0, SEEK_SET);
            dbg2("first seq written");
            break;
        }


So help message should be like "create /dev/mdev.seq at boot containing
one new line only"