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

On Fri, Feb 22, 2019 at 03:31:57PM +1100, Oliver wrote:

On Fri, Feb 22, 2019 at 2:24 PM Sam Bobroff [off-list ref] wrote:

quoted

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.

quoted

Cheers,
Sam.

On Thu, Feb 14, 2019 at 04:14:42PM +1100, Sam Bobroff wrote:

quoted

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 <redacted>
---
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