Couldn't register serial port 0000:02:0a.2: -28

I run into a problem where I have a device which has two normal serial ports and some on a PCI device.
After booting the kernel I got this error line:

Couldn't register serial port 0000:02:0a.2: -28

In order to get more than 2 serial ports working, I “fixed” my currently used kernel config:

CONFIGSERIAL8250NRUARTS=32 CONFIGSERIAL8250RUNTIMEUARTS=6

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