[CentOS] How to blacklist a device driver (sysemd)

Hi,

how can a specific device driver in CentOS 7 be blacklisted, so that it 
doesn't load at boot time?  We have Infiniband adapters which are not 
completely supported by CentOS and we want to silence the error messages 
for the time being.

I tried with the files

   /etc/modprobe.d/blacklist
   /etc/modprobe.d/blacklist.conf

and with entries

   mlx5_core
   mlx5_ib

   blacklist mlx5_core
   blacklist mlx5_ib

   install mlx5_core /dev/null
   install mlx5_ib /dev/null

all found on different websites.

None of these entries helps.  mlx5_core and mlx5_ib are still loaded and 
the system is flooded with error messages.

Cheers
frank