[Resending due to no response to the original message in a week] Hi all, I have a board with a BIOS bug that reports the following I/O port regions in _CRS on one of the host bridges: 0x0000-0x03af // #0 0x03e0-0x0cf7 // #1 0x03b0-0x03bb // #2 0x03c0-0x03df // #3 0x0000-0xdfff // #4 0xf000-0xffff // #5 Obviously, region number #4 is erroneous as it overlaps with regions #0..3. The code in coalesce_windows() in arch/x86/pci/acpi.c attempts to recover from such kind of BIOS bugs by merging the overlapping regions. Current code expands region #0 to 0x0000-0xdffff and makes region #4 ignored. As a result, overlap of the expanded region #0 with regions #1..3 remains undetected (as the inner loop already compared them with region #0). As a result, regions #1..3 are inserted into the resource tree even though they overlap with adjusted region #0 - which later results in resource conflicts for PCI devices with IO ports in one of those regions (e.g., for an PCI IDE controller in legacy mode - which has port 0x3f6). The kernel then refuses to initialize these devices. The fix: instead of expanding res1 and ignoring res2, do the opposite. The res2 window is yet to be compared against all windows between res1 and res2 (regions #1..3 in the above example), so the resulting resource map will include just the expanded region - and will ignore any overlapping ones. Signed-off-by: Alexey Neyman