Define SPI bus number

Hello all,
I working on a kernel module for a SPI device. I add a altera softIP in Qsys and connect it over the h2f_axi_master at address 0x0005 0000.
I use the spi-altera driver for the SPI interface. So, this device driver give me a spi_master on the Linux side. Currently, the SPI master is shown in Linux as “spi32765”. My question is, from where is the number “32765” from and would it be a fix number?
I saw in the spi-altera sources, the assignment: master->bus_num = pdev->id;
But where is the pdev->id defined? I couldn’t find more information for this… Do someone know this? And is it possible to define this to fix, custom value during boot process?
At the end, I would have multiple SPI masters on the device and each should have a fix number for the identification…