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

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Date:   Thu, 25 Aug 2022 17:49:28 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Pali Rohár <pali@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     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 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.

cheers


> Fixes: 566356813082 ("powerpc/pci: Add config option for using all 256 PCI buses")
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>  arch/powerpc/kernel/pci_32.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/arch/powerpc/kernel/pci_32.c b/arch/powerpc/kernel/pci_32.c
> index ffc4e1928c80..8acbc9592ebb 100644
> --- a/arch/powerpc/kernel/pci_32.c
> +++ b/arch/powerpc/kernel/pci_32.c
> @@ -249,6 +249,15 @@ static int __init pcibios_init(void)
>  
>  	printk(KERN_INFO "PCI: Probing PCI hardware\n");
>  
> +#ifdef CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
> +	/*
> +	 * Enable PCI domains in /proc when PCI bus numbers are not unique
> +	 * across all PCI domains to prevent conflicts. And keep PCI domain 0
> +	 * backward compatible in /proc for video cards.
> +	 */
> +	pci_add_flags(PCI_ENABLE_PROC_DOMAINS | PCI_COMPAT_DOMAIN_0);
> +#endif
> +
>  	if (pci_has_flag(PCI_REASSIGN_ALL_BUS))
>  		pci_assign_all_buses = 1;
>  
> -- 
> 2.20.1