linux-kernel - Re: [PATCH] powerpc/pci: Enable PCI domains in /proc when PCI bus numbers are not unique

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Message-ID: <87wnanu4vf.fsf@mpe.ellerman.id.au>
Date:   Thu, 01 Sep 2022 13:53:56 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Pali Rohár <pali@...nel.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/pci: Enable PCI domains in /proc when PCI bus
 numbers are not unique

Pali Rohár <pali@...nel.org> writes:
> On Thursday 25 August 2022 17:49:28 Michael Ellerman wrote:
>> Pali Rohár <pali@...nel.org> writes:
>> > On 32-bit powerpc systems with more PCIe controllers and more PCI domains,
>> > where on more PCI domains are same PCI numbers, when kernel is compiled
>> > with CONFIG_PROC_FS=y and CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT=y
>> > options, kernel prints "proc_dir_entry 'pci/01' already registered" error
>> > message.
>> 
>> Thanks, I'll pick this up.
>> 
>> > This regression started appearing after commit 566356813082 ("powerpc/pci:
>> > Add config option for using all 256 PCI buses") in case in each mPCIe slot
>> > is connected PCIe card and therefore PCI bus 1 is populated in for every
>> > PCIe controller / PCI domain.
>> >
>> > The reason is that PCI procfs code expects that when PCI bus numbers are
>> > not unique across all PCI domains, function pci_proc_domain() returns true
>> > for domain dependent buses.
>> >
>> > Fix this issue by setting PCI_ENABLE_PROC_DOMAINS and PCI_COMPAT_DOMAIN_0
>> > flags for 32-bit powerpc code when CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
>> > is enabled. Same approach is already implemented for 64-bit powerpc code
>> > (where PCI bus numbers are always domain dependent).
>> 
>> We also have the same in ppc4xx_pci_find_bridges().
>> 
>> And if we can eventually make CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
>> the standard behaviour on 32-bit then everything would behave the same
>> and we could simplify pci_proc_domain() to match what other arches do.
>
> I sent two patches which do another steps to achieve it:
> https://lore.kernel.org/linuxppc-dev/20220817163927.24453-1-pali@kernel.org/t/#u
>
> Main blocker is pci-OF-bus-map which is in direct conflict with
> CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT and which used on chrp and pmac.
> And I have no idea if pci-OF-bus-map is still needed or not.

Yeah thanks, I saw those patches.

I can't find any code that refers to pci-OF-bus-map, so I'm inclined to
remove it entirely.

But I'll do some more searching to see if I can find any references to
it in old code.

cheers