[PATCH 00/10] PCI: Improve head free space usage

[Bjorn Helgaas]

[+cc Xifer; thanks very much for reporting and testing!]

On Tue, Mar 24, 2026 at 06:56:23PM +0200, Ilpo Järvinen wrote:
> Hi all,
> 
> This series attempts to take advantage of free head space (the free
> space before the aligned start address) in order to generally produce a
> tighter packing of the resources/bridge windows.
> 
> The recent changes to the resource fitting algorithm caused resource
> allocation failures in some cases where a bridge window that is sized
> to be gapless could no longer be assigned. The previous algorithm left
> a huge gaps which allowed it to place the remainder (non-aligning part
> of the size) before the start address of used for the gapless fit,
> whereas the new gapless approach always had to place the remainder
> after the aligning part of the resources. There is not always space
> for the remainder triggering those failures (e.g., when the aligning
> part must be placed at the top of the window).
> 
> This series attempts to allow placing the remainder once again before
> the aligning part, but now without leaving huge gaps to retain the
> benefits of the gapless bridge windows. The approach is somewhat hacky
> but should work thanks to PCI resources fundamentally consisting only
> power-of-two atoms.
> 
> There maybe cases where architecture would not want to do such
> relocation. This series adds the relocation to arch
> pcibios_align_resource() functions to allow all of them taking
> advantage of the better resource packing but if somebody objects doing
> this relocation for a particular arch, I can remove it, please just let
> me know (this relocation doesn't seem critical unless there are
> regressions).
> 
> Ilpo Järvinen (10):
>   resource: Add __resource_contains_unbound() for internal contains
>     checks
>   resource: Pass full extent of empty space to resource_alignf CB
>   resource: Rename 'tmp' variable to 'full_avail'
>   ARM/PCI: Remove unnecessary second application of align
>   am68k/PCI: Remove unnecessary second application of align
>   MIPS: PCI: Remove unnecessary second application of align
>   parisc/PCI: Cleanup align handling
>   PCI: Rename window_alignment() to pci_min_window_alignment()
>   PCI: Align head space better
>   PCI: Fix alignment calculation for resource size larger than align
> 
>  arch/alpha/kernel/pci.c          |  1 +
>  arch/arm/kernel/bios32.c         |  9 ++++---
>  arch/m68k/kernel/pcibios.c       |  8 +++++--
>  arch/mips/pci/pci-generic.c      |  8 ++++---
>  arch/mips/pci/pci-legacy.c       |  3 +++
>  arch/parisc/kernel/pci.c         | 17 ++++++++------
>  arch/powerpc/kernel/pci-common.c |  6 ++++-
>  arch/s390/pci/pci.c              |  1 +
>  arch/sh/drivers/pci/pci.c        |  6 ++++-
>  arch/x86/pci/i386.c              |  5 +++-
>  arch/xtensa/kernel/pci.c         |  3 +++
>  drivers/pci/pci.h                |  3 +++
>  drivers/pci/setup-bus.c          | 15 ++++++++----
>  drivers/pci/setup-res.c          | 40 +++++++++++++++++++++++++++++++-
>  drivers/pcmcia/rsrc_nonstatic.c  |  3 ++-
>  include/linux/ioport.h           | 22 +++++++++++++++---
>  include/linux/pci.h              | 12 +++++++---
>  kernel/resource.c                | 33 +++++++++++++-------------
>  18 files changed, 149 insertions(+), 46 deletions(-)

I added Xifer's tested-by, fixed the "am68k" and missing "if"
typos, and applied these to pci/resource for v7.1.

Ilpo, if you post a v2 with more changes, I'll update to it.  I
applied the series now to get a head start on 0-day building and into
next.