Re: [PATCH] PCI: host-common: Request bus reassignment when not probe-only

[Manivannan Sadhasivam]

On Fri, Apr 10, 2026 at 07:51:24PM +0530, Ratheesh Kannoth wrote:
> pci_host_common_init() is used by several generic ECAM host drivers.
> After PCI core changes around pci_flags and preserve_config, these hosts
> no longer opted into full bus number reassignment the way they did
> before.
> 

So pci_assign_unassigned_root_bus_resources() only assigns the unclaimed
resources, and do not reassign the bus numbers. Probably the offending commit
confused PCI_REASSIGN_ALL_BUS with PCI_REASSIGN_ALL_RSRC.

> When PCI_PROBE_ONLY is not set, add PCI_REASSIGN_ALL_BUS so
> pci_scan_bridge_extend() takes the reassignment path: bus numbers can be
> assigned from firmware EA data (e.g. pci_ea_fixed_busnrs()). Skip the
> flag in probe-only mode so existing assignments are not overridden.
> 
> CC: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> CC: Vidya Sagar <vidyas@xxxxxxxxxx>
> Fixes: 7246a4520b4b ("PCI: Use preserve_config in place of pci_flags")
> Link: https://lore.kernel.org/netdev/adcXzcz2wWJFw4d7@rkannoth-OptiPlex-7090/
> Signed-off-by: Ratheesh Kannoth <rkannoth@xxxxxxxxxxx>
> ---
>  drivers/pci/controller/pci-host-common.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index d6258c1cffe5..860783553cca 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -68,6 +68,10 @@ int pci_host_common_init(struct platform_device *pdev,
>  	if (IS_ERR(cfg))
>  		return PTR_ERR(cfg);
>  
> +	/* Do not reassign resources if probe only */

This comment is still wrong and could be the source of confusion that lead to
the bug. PCI_REASSIGN_ALL_BUS only reassigns the bus number, not resources. So
please reword it.

> +	if (!pci_has_flag(PCI_PROBE_ONLY))
> +		pci_add_flags(PCI_REASSIGN_ALL_BUS);

This forces bus number reassignment for all platforms whose DT doesn't provide
'linux,probe-only' property. Maybe that's OK given that this was the behavior
before 7246a4520b4b. 

- Mani

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