linux-kernel - Re: [PATCH 1/1] pci: Add subordinate check before pci_add_new

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Message-ID: <64025ba8-948a-4d91-8fc6-a1ede807ca8d@gmail.com>
Date: Sun, 17 Aug 2025 10:46:08 +0800
From: Ethan Zhao <etzhao1900@...il.com>
To: Rui He <rui.he@...driver.com>, Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 Prashant.Chikhalkar@...driver.com, Jiguang.Xiao@...driver.com
Subject: Re: [PATCH 1/1] pci: Add subordinate check before pci_add_new_bus()



On 8/14/2025 5:39 PM, Rui He wrote:
> For preconfigured PCI bridge, child bus created on the first scan.
> While for some reasons(e.g register mutation), the secondary, and subordiante
> register reset to 0 on the second scan, which caused to create
> PCI bus twice for the same PCI device.
> 
> Following is the related log:
> [Wed May 28 20:38:36 CST 2025] pci 0000:0b:01.0: PCI bridge to [bus 0d]
> [Wed May 28 20:38:36 CST 2025] pci 0000:0b:05.0: bridge configuration invalid ([bus 00-00]), reconfiguring
> [Wed May 28 20:38:36 CST 2025] pci 0000:0b:01.0: PCI bridge to [bus 0e-10]
> [Wed May 28 20:38:36 CST 2025] pci 0000:0b:05.0: PCI bridge to [bus 0f-10]
Could you help to attach a 'lspci -t' about the topology ?
bridge 0000:0b:01.0 and 0000:0b:05.0 have the same subordinate
bus number, that is weird seems they aren't connected as upstream
and downstream, but siblings.

Does the device behind the bridge 0000:0b:05.0 work after the
second scan (TLP are forwarded) ?>
> Here PCI device 000:0b:01.0 assigend to bus 0d and 0e.
> 
> This patch checks if child PCI bus has been created on the second scan
> of bridge. If yes, return directly instead of create a new one.
> 
> Signed-off-by: Rui He <rui.he@...driver.com>
> ---
>   drivers/pci/probe.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index f41128f91ca76..ec67adbf31738 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1444,6 +1444,9 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
>   			goto out;
>   		}
>   
The bridge should was marked as broken=1 already, bailed out earlier, 
wouldn't get here with bridge forwarding was disabled. no further 
configuration anymore. what is your kernel number ?


Thanks,
Ethan> +		if(pci_has_subordinate(dev))
> +			goto out;
> +
>   		/* Clear errors */
>   		pci_write_config_word(dev, PCI_STATUS, 0xffff);
>