I was try to install cardbus pccard with realtek 8139 chip on board. Card was detected fine, but does not work:
#l0: rtl8139: 10Mbps port 0x400 irq 11: FFFFFFFFFFFF
pci output:
...
9.0.0:  02.00.00 10ec/8139  11 0:00000401 256 1:04000000 512       ...            
                                                                                
xd /dev/pci/9.0.0raw output:                                                            
0000000  ec103981 04009002 10000002 00400000
...
as You can see - memory and io on bus are disabled: On boot, original devpccard.c correctly enable bus master, memory and io, but leave pci->pcr don't touched. in my case it was 0. pcisetbme call from ether8139.c leave pccard out of luck. 

P.S. cls and ltr registers are filled for consistency too.