Re: [PATCH 1/1] powerpc/64: Adjust order in pcibios_init()

[Sam Bobroff <sbobroff@linux.ibm.com>]

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On Fri, Feb 22, 2019 at 03:31:57PM +1100, Oliver wrote:
> On Fri, Feb 22, 2019 at 2:24 PM Sam Bobroff <sbobroff@linux.ibm.com> wrote:
> >
> > Hey all,
> >
> > After some consideration, I've decided to post a v2 of this patch that
> > will make it a bit safer (although I haven't seen any problems with it)
> > and make it a little easier to refactor some of the EEH code that
> > interacts with the hooks.
> 
> Can you be a little more specific?

Sure:

When the original patch moves pci_bus_add_devices() to after
pcibios_resource_survey(), this also causes the pcibios_fixup hook
to move, because it's called at the end of pcibios_resource_survey().

So pcibios_fixup would run before pcibios_bus_add_device and while I
don't think that will actually cause problems, there doesn't seem to be
any reason to change the order either. So, I think it would be better
to extract the pcibios_fixup hook out of pcibios_resource_survey() and
call it from pcibios_init after the devices are added, preserving that
ordering.

That's the general reasoning but more specifically, I want to refactor
the EEH code around adding devices, and it seems like I'm going to
need the handlers in that order so that pcibios_bus_add_device() can
probe for EEH support in devices before the EEH post init code needs to
know if any were found.

> > Cheers,
> > Sam.
> >
> > On Thu, Feb 14, 2019 at 04:14:42PM +1100, Sam Bobroff wrote:
> > > The pcibios_init() function for 64 bit PowerPC currently calls
> > > pci_bus_add_devices() before pcibios_resource_survey(), which seems
> > > incorrect because it adds devices and attempts to bind their drivers
> > > before allocating their resources (although no problems seem to be
> > > apparent).
> > >
> > > So move the call to pci_bus_add_devices() to after
> > > pcibios_resource_survey().
> > >
> > > This will also allow the ppc_md.pcibios_bus_add_device() hooks to
> > > perform actions that depend on PCI resources, both during rescanning
> > > (where this is already the case) and at boot time, which should
> > > support improvements and refactoring.
> > >
> > > Signed-off-by: Sam Bobroff <sbobroff@linux.ibm.com>
> > > ---
> > > Hi everyone,
> > >
> > > I've tested this on a P9 for both the host and a KVM guest, and the change
> > > hasn't caused any differences in PCI resource assignments or the general boot
> > > messages.
> > >
> > > I've also had a go at inspecting most of the code used by pci_bus_add_devices()
> > > and pcibios_resource_survey() and it doesn't look like there are going to be
> > > any changes in behaviour caused by reordering.  It might be worth mentioning
> > > that the hotplug path (see pcibios_finish_adding_to_bus()) already does
> > > resource allocation before calling pci_bus_add_devices().
> > >
> > > However, it would be great if someone could test this change on some older
> > > hardware or comment on wether we should make the same change on 32 bit machines.
> > >
> > > Cheers,
> > > Sam.
> > >
> > >  arch/powerpc/kernel/pci_64.c | 8 +++++---
> > >  1 file changed, 5 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/powerpc/kernel/pci_64.c b/arch/powerpc/kernel/pci_64.c
> > > index 9d8c10d55407..1ce28888dbdb 100644
> > > --- a/arch/powerpc/kernel/pci_64.c
> > > +++ b/arch/powerpc/kernel/pci_64.c
> > > @@ -58,14 +58,16 @@ static int __init pcibios_init(void)
> > >       pci_add_flags(PCI_ENABLE_PROC_DOMAINS | PCI_COMPAT_DOMAIN_0);
> > >
> > >       /* Scan all of the recorded PCI controllers.  */
> > > -     list_for_each_entry_safe(hose, tmp, &hose_list, list_node) {
> > > +     list_for_each_entry_safe(hose, tmp, &hose_list, list_node)
> > >               pcibios_scan_phb(hose);
> > > -             pci_bus_add_devices(hose->bus);
> > > -     }
> > >
> > >       /* Call common code to handle resource allocation */
> > >       pcibios_resource_survey();
> > >
> > > +     /* Add devices. */
> > > +     list_for_each_entry_safe(hose, tmp, &hose_list, list_node)
> > > +             pci_bus_add_devices(hose->bus);
> > > +
> > >       printk(KERN_DEBUG "PCI: Probing PCI hardware done\n");
> > >
> > >       return 0;
> > > --
> > > 2.19.0.2.gcad72f5712
> > >
> 

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