I have encountered a problem with a box with many PCI devices. During 
boot the kernel reports "PCI: Cannot allocate resource region 0 of 
device xx:yy:zz" as can be seen in the attached dmesg.

Analyzing the output of lspci it seems that the problem is due to lack 
of I/O space. A lot
of I/O space is used by the stuff on the mainboard and each PCI bridge 
is allocated 8k
of I/O space so by the time I reach PCI bridge number 4 no further I/O 
ports can be
found.

I have read that PCI bridge I/O space must be allocated in 4k blocks so 
it seems it should
be possible to cut space used by each bridge in half, provided that the 
I/O ranges behind
the bridge will fit in 4k. In this case I have 4 devices and a total of 
6 I/O ranges behind
each bridge with two of the ranges 16 bytes long and 4 32 bytes long. 
These are configured
at 1k intervals and hence the need for 8k on the bridge instead of 4k.

I have tried to use setpci to remap the devices by taking the devices 
behind one of the
correctly configured bridges and remapping the 6 I/O ranges at 256byte 
intervals instead of
1k and then shrinking the I/O region for the bridge to 4k. I have also 
assigned the I/O space
freed by the previous operation to one of the incorrectly configured 
bridges and mapped the
I/O ranges for the devices behind this bridge to 256byte intervals. This 
approach seems at
least somewhat successfull, but it causes other problems since changing 
the bridge and
device configuration with setpci does not change the kernel structures 
representing the
pci devices - this causes problems when loading a driver for the modules.

Any suggestions on how to fix this problem are highly appreciated.

\Lars Knudsen