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References: <f232553753fe148118646c9013a3d962c19b58ec.1550121250.git.sbobroff@linux.ibm.com>
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From: Oliver <oohall@gmail.com>
Date: Fri, 15 Feb 2019 11:46:34 +1100
Message-ID: <CAOSf1CHnCiykoAZ_qAfNGTXmVUL=BMQkYkV33sQWXDgeeUvL0g@mail.gmail.com>
Subject: Re: [PATCH 1/1] powerpc/64: Adjust order in pcibios_init()
To: Sam Bobroff <sbobroff@linux.ibm.com>
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On Thu, Feb 14, 2019 at 4:14 PM Sam Bobroff <sbobroff@linux.ibm.com> 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>

Reviewed-by: Oliver O'Halloran <oohall@gmail.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
>