[PATCH] ARM64: PCI: do not enable resources on PROBE_ONLY systems

[Lorenzo Pieralisi]

Hi Bjorn,

On Fri, Aug 28, 2015 at 10:14:44PM +0100, Bjorn Helgaas wrote:
> Hi Lorenzo,
> 
> On Thu, Jul 30, 2015 at 02:13:59PM +0100, Lorenzo Pieralisi wrote:
> > On ARM64 PROBE_ONLY PCI systems resources are not currently claimed,
> > therefore they can't be enabled since they do not have a valid
> > parent pointer; this in turn prevents enabling PCI devices on
> > ARM64 PROBE_ONLY systems, causing PCI devices initialization to
> > fail.
> 
> Where does arm64 claim PCI BAR resources for the non-PROBE_ONLY case?

arm64 (and arm) does not claim resources in arch code, they are always
assigned in the respective host controllers (or the pcibios on arm),
except for the PCI generic host when in PROBE_ONLY mode, where resources
are neither claimed nor assigned (the reason for this patch to exist).

Certainly something to consolidate as part of the rework we talked
about at LPC (PCI ACPI probing is yet another reason to consolidate it).

I am working on this, in particular I want to test how claiming the
resources by default will impact ARM systems.

For the records, Will kindly provided me with an Alpha box so that I can
test on it too.

> I know it must be there somewhere, but I don't see it.

It is not there, it is done in the host controllers by assigning the
resources (which also "claim" them by assigning the parent pointer).

Thanks,
Lorenzo

> 
> > To solve this issue, resources must be claimed when devices are
> > added on PROBE_ONLY systems, which ensures that the resource hierarchy
> > is validated and the resource tree is sane, but this requires changes
> > in the ARM64 resource management that can affect adversely existing
> > PCI set-ups (claiming resources on !PROBE_ONLY systems might break
> > existing ARM64 PCI platform implementations).
> > 
> > As a temporary solution in preparation for a proper resources claiming
> > implementation in ARM64 core, to enable PCI PROBE_ONLY systems on ARM64,
> > this patch adds a pcibios_enable_device() arch implementation that
> > simply prevents enabling resources on PROBE_ONLY systems (mirroring ARM
> > behaviour).
> > 
> > This is always a safe thing to do because on PROBE_ONLY systems the
> > configuration space set-up can be considered immutable, and it is in
> > preparation of proper resource claiming that would finally validate
> > the PCI resources tree in the ARM64 arch implementation on PROBE_ONLY
> > systems.
> > 
> > For !PROBE_ONLY systems resources enablement in pcibios_enable_device()
> > on ARM64 is implemented as in current PCI core, leaving the behaviour
> > unchanged.
> > 
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> > Cc: Will Deacon <will.deacon at arm.com>
> > Cc: Bjorn Helgaas <bhelgaas at google.com>
> > Cc: Catalin Marinas <catalin.marinas at arm.com>
> > ---
> > Bjorn, all,
> > 
> > as I mention in the commit log, this patch is a temporary solution
> > in preparation for proper resources claiming in ARM64, so that
> > we can safely enable the PCI generic host controller on ARM64 systems.
> > 
> > It mirrors ARM implementation and I will work on changing both
> > ARM and ARM64 to convert them to proper resources claiming in
> > the respective implementations.
> > 
> > Lorenzo
> > 
> >  arch/arm64/kernel/pci.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> > index 4095379..b3d098b 100644
> > --- a/arch/arm64/kernel/pci.c
> > +++ b/arch/arm64/kernel/pci.c
> > @@ -38,6 +38,19 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> >  	return res->start;
> >  }
> >  
> > +/**
> > + * pcibios_enable_device - Enable I/O and memory.
> > + * @dev: PCI device to be enabled
> > + * @mask: bitmask of BARs to enable
> > + */
> > +int pcibios_enable_device(struct pci_dev *dev, int mask)
> > +{
> > +	if (pci_has_flag(PCI_PROBE_ONLY))
> > +		return 0;
> > +
> > +	return pci_enable_resources(dev, mask);
> > +}
> > +
> >  /*
> >   * Try to assign the IRQ number from DT when adding a new device
> >   */
> > -- 
> > 2.2.1
> > 
>