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Subject[PATCH v5 0/9] PCI: allocate space top-down, not bottom-up
When we move PCI devices, we currently allocate space bottom-up, i.e., we look
at PCI bus resources in the order we found them, we look at gaps between child
resources bottom-up, and we align the new space at the bottom of an available

On x86, we move PCI devices more than we used to because we now pay attention
to the PCI host bridge windows from ACPI. For example, when we find a device
that's outside all the known host bridge windows, we try to move it into a
window, and we look for space starting at the bottom.

Windows does similar device moves, but it looks for space top-down rather than
bottom-up. Since most machines are better-tested with Windows than Linux, this
difference means that Linux is more likely to trip over BIOS bugs in the PCI
host bridge window descriptions than Windows is.

We've had several reports of Dell machines where the BIOS leaves the AHCI
controller outside the host bridge windows (BIOS bug #1), *and* the lowest
host bridge window includes an area that doesn't actually reach PCI (BIOS
bug #2). The result is that Windows (which moves AHCI to the top of a window)
works fine, while Linux (which moves AHCI to the bottom, buggy, area) doesn't

These patches change Linux to allocate space more like Windows does:

1) The x86 pcibios_align_resource() will choose space from the
end of an available area, not the beginning.

2) In the generic allocate_resource() path, we'll look for space
between existing children from the top, not from the bottom.

3) When pci_bus_alloc_resource() looks for available space, it
will start from the highest window, not the first one we found.

This series fixes a 2.6.34 regression that prevents many Dell Precision
workstations from booting:

Changes from v4 to v5:
- Fix for
reported by Fabrice Bellet <>
- Declutter find_resource().
- Catch overflow of "ALIGN(tmp.start)".

Changes from v3 to v4:
- Use round_down() rather than adding ALIGN_DOWN().
- Replace ARCH_HAS_TOP_DOWN_ALLOC #define with a boot-time architecture
choice and add a "resource_alloc_from_bottom" command line option to
revert to the old behavior (NOTE: this only affects allocate_resource(),
not pcibios_align_resource() or pci_bus_alloc_resource()).
- Fixed find_resource_from_top() again; it still didn't handle a child
that ended at the parent's end correctly.

Changes from v2 to v3:
- Fixes for
reported by Horst H. von Brand <>
- Updated iomem_resource.end to reflect the end of usable physical address
space. Otherwise, we might allocate right up to 0xffffffff_ffffffff,
which isn't usable.
- Make allocate_resource() change conditional on ARCH_HAS_TOP_DOWN_ALLOC.
Without arch-specific changes like the above, it's too dangerous to
make this change for everybody at once.
- Fix 64-bit wraparound in find_resource(). If the last child happened
to end at ~0, we computed the highest available space as [child->end + 1,
root->end], which makes us think the available space started at 0,
which makes us return space that may already be allocated.

Changes from v1 to v2:
- Moved check for allocating before the available area from
pcibios_align_resource() to find_resource(). Better to do it
after the alignment callback is done, and make it generic.
- Fixed pcibios_align_resource() alignment. If we start from the
end of the available area, we must align *downward*, not upward.
- Fixed pcibios_align_resource() ISA alias avoidance. Again, since
the starting point is the end of the area, we must align downward
when we avoid aliased areas.

Bjorn Helgaas (9):
resources: add a default alignf to simplify find_resource()
resources: factor out resource_clip() to simplify find_resource()
resources: ensure callback doesn't allocate outside available space
resources: handle overflow when aligning start of available area
resources: support allocating space within a region from the top down
PCI: allocate bus resources from the top down
x86/PCI: allocate space from the end of a region, not the beginning
x86: update iomem_resource end based on CPU physical address capabilities
x86: allocate space within a region top-down

Documentation/kernel-parameters.txt | 5 +
arch/x86/kernel/setup.c | 2
arch/x86/pci/i386.c | 17 +++-
drivers/pci/bus.c | 53 +++++++++++-
include/linux/ioport.h | 1
kernel/resource.c | 151 +++++++++++++++++++++++++++++++----
6 files changed, 202 insertions(+), 27 deletions(-)

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