Re: [PATCH v2 1/8] x86/PCI: prevent re-allocation of already existing bridge and ROM resources

[Bjorn Helgaas <bhelgaas@google.com>]

On Wed, Jul 3, 2013 at 8:04 AM, Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
> In hotplug case (especially with Thunderbolt enabled systems) we might need
> to call pcibios_resource_survey_bus() several times for a bus. The function
> ends up calling pci_claim_resource() for each bridge resource that then
> fails claiming that the resource exists already (which it does). Once this
> happens the resource is invalidated thus preventing devices behind the
> bridge to allocate their resources.
>
> To fix this we do what has been done in pcibios_allocate_dev_resources()
> and check 'parent' of the given resource. If it is non-NULL it means that
> the resource has been allocated already and we can skip it. We do the same
> for ROM resources as well.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

This looks reasonable to me.

However, the use of "r->parent" to determine whether the resource is
already allocated is nothing specific to x86.  So I think we might be
missing an opportunity to make this more consistent across
architectures.  I looked at other callers of pci_claim_resource() for
bridge and ROM resources, and it looks like we might be able to make
similar changes in:

  frv pcibios_allocate_bus_resources()
  ia64 pcibios_fixup_resources() (via pcibios_fixup_bridge_resources())
  mn10300 pcibios_allocate_bus_resources()
  mn10300 pcibios_assign_resources() (ROM)
  mn10300 pcibios_fixup_device_resources()
  parisc lba_fixup_bus()

I really hate the idea of fixing something for x86 but not for other
arches, so maybe somebody could take a deeper look at this and see if
it would make sense to change the other arches, too.

Bjorn

> ---
>  arch/x86/pci/i386.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
> index 94919e3..db6b1ab 100644
> --- a/arch/x86/pci/i386.c
> +++ b/arch/x86/pci/i386.c
> @@ -210,6 +210,8 @@ static void pcibios_allocate_bridge_resources(struct pci_dev *dev)
>                 r = &dev->resource[idx];
>                 if (!r->flags)
>                         continue;
> +               if (r->parent)  /* Already allocated */
> +                       continue;
>                 if (!r->start || pci_claim_resource(dev, idx) < 0) {
>                         /*
>                          * Something is wrong with the region.
> @@ -318,6 +320,8 @@ static void pcibios_allocate_dev_rom_resource(struct pci_dev *dev)
>         r = &dev->resource[PCI_ROM_RESOURCE];
>         if (!r->flags || !r->start)
>                 return;
> +       if (r->parent) /* Already allocated */
> +               return;
>
>         if (pci_claim_resource(dev, PCI_ROM_RESOURCE) < 0) {
>                 r->end -= r->start;
> --
> 1.8.3.2
>