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

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Date:   Thu, 1 Sep 2022 09:24:49 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>
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

On Thursday 01 September 2022 13:53:56 Michael Ellerman wrote:
> 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

>From the code itself I have feeling that some external programs or maybe
some firmware can access or use this property. But I have really no idea.