Re: [PATCH v2 0/4] PCI: allocate space top-down, not bottom-up

[Bjorn Helgaas <bjorn.helgaas@hp.com>]

Added cc: stable@kernel.org
See:
  https://patchwork.kernel.org/patch/189182/
  https://patchwork.kernel.org/patch/189232/
  https://patchwork.kernel.org/patch/189242/
  https://patchwork.kernel.org/patch/189252/

On Friday, September 17, 2010 04:32:06 pm Bjorn Helgaas wrote:
> 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
> region.
> 
> 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
> work.
> 
> 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:
> 
>     https://bugzilla.kernel.org/show_bug.cgi?id=16228
> 
> 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 (4):
>       resources: ensure alignment callback doesn't allocate below available start
>       x86/PCI: allocate space from the end of a region, not the beginning
>       resources: allocate space within a region from the top down
>       PCI: allocate bus resources from the top down
> 
> 
>  arch/x86/pci/i386.c |   18 ++++++++++++-----
>  drivers/pci/bus.c   |   53 ++++++++++++++++++++++++++++++++++++++++++++++-----
>  kernel/resource.c   |   50 +++++++++++++++++++++++++++++++-----------------
>  3 files changed, 92 insertions(+), 29 deletions(-)
>