linux-kernel - Re: [PATCH 5/5] powerpc/pci: Add config option for using all 256 PCI buses

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Message-ID: <20220721222145.rzgthbwoselx2l43@pali>
Date:   Fri, 22 Jul 2022 00:21:45 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Cédric Le Goater <clg@...d.org>,
        Nick Child <nick.child@....com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] powerpc/pci: Add config option for using all 256 PCI
 buses

On Wednesday 06 July 2022 12:43:08 Pali Rohár wrote:
> By default on PPC32 are PCI bus numbers unique across all PCI domains.
> So system could have only 256 PCI buses independently of available
> PCI domains.
> 
> This is due to filling DT property pci-OF-bus-map which does not reflect
> multi-domain setup.
> 
> On all powerpc platforms except chrp and powermac there is no DT property
> pci-OF-bus-map anymore and therefore it is possible on non-chrp/powermac
> platforms to avoid this limitation of maximal number of 256 PCI buses in
> system even on multi-domain setup.
> 
> But avoiding this limitation would mean that all PCI and PCIe devices would
> be present on completely different BDF addresses as every PCI domain starts
> numbering PCI bueses from zero (instead of the last bus number of previous
> enumerated PCI domain). Such change could break existing software which
> expects fixed PCI bus numbers.
> 
> So add a new config option CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT which
> enables this change. By default it is disabled. It cause that initial value
> of hose->first_busno is zero.
> 
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>  arch/powerpc/Kconfig         | 11 +++++++++++
>  arch/powerpc/kernel/pci_32.c |  6 ++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index be68c1f02b79..f66084bc1dfe 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -370,6 +370,17 @@ config PPC_DCR
>  	depends on PPC_DCR_NATIVE || PPC_DCR_MMIO
>  	default y
>  
> +config PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
> +	depends on PPC32
> +	depends on !PPC_PMAC && !PPC_CHRP
> +	bool "Assign PCI bus numbers from zero individually for each PCI domain"
> +	help
> +	  By default on PPC32 were PCI bus numbers unique across all PCI domains.
> +	  So system could have only 256 PCI buses independently of available
> +	  PCI domains. When this option is enabled then PCI bus numbers are
> +	  PCI domain dependent and each PCI controller on own domain can have
> +	  256 PCI buses, like it is on other Linux architectures.
> +

What do you think, would it be possible to set default value of this
option to enabled?

>  config PPC_OF_PLATFORM_PCI
>  	bool
>  	depends on PCI
> diff --git a/arch/powerpc/kernel/pci_32.c b/arch/powerpc/kernel/pci_32.c
> index 2f7284b68f06..433965bf37b4 100644
> --- a/arch/powerpc/kernel/pci_32.c
> +++ b/arch/powerpc/kernel/pci_32.c
> @@ -239,7 +239,9 @@ void pcibios_setup_phb_io_space(struct pci_controller *hose)
>  static int __init pcibios_init(void)
>  {
>  	struct pci_controller *hose, *tmp;
> +#ifndef CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
>  	int next_busno = 0;
> +#endif
>  
>  	printk(KERN_INFO "PCI: Probing PCI hardware\n");
>  
> @@ -248,13 +250,17 @@ static int __init pcibios_init(void)
>  
>  	/* Scan all of the recorded PCI controllers.  */
>  	list_for_each_entry_safe(hose, tmp, &hose_list, list_node) {
> +#ifndef CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
>  		if (pci_assign_all_buses)
>  			hose->first_busno = next_busno;
> +#endif
>  		hose->last_busno = 0xff;
>  		pcibios_scan_phb(hose);
>  		pci_bus_add_devices(hose->bus);
> +#ifndef CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
>  		if (pci_assign_all_buses || next_busno <= hose->last_busno)
>  			next_busno = hose->last_busno + pcibios_assign_bus_offset;
> +#endif
>  	}
>  
>  #if defined(CONFIG_PPC_PMAC) || defined(CONFIG_PPC_CHRP)
> -- 
> 2.20.1
>