Re: [PATCH v2 2/2] PCI: Add pci=nodpc kernel boot option

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The `pci=nodpc` parameter disables native OS DPC but still claims DPC control via ACPI `_OSC` and enables it via `_DSM`, causing permanent unhandled link errors.
--

--- Patch [2]: [PATCH v2 2/2] PCI: Add pci=nodpc kernel boot option ---
commit 9eea006773bbca0de0b0f501e83971ad7b74166e
Author: Yury Murashka <yurypm@arista.com>

PCI: Add pci=nodpc kernel boot option

This patch introduces the pci=nodpc kernel boot option to disable PCI
Downstream Port Containment (DPC). When specified, DPC initialization,
state operations, and driver registration are bypassed, allowing userspace
to handle PCIe errors.

> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> index 2b779bd1d861b..759d9f18812ee 100644
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
[ ... ]
> @@ -404,6 +411,9 @@ void pci_dpc_init(struct pci_dev *pdev)
>  {
>  	u16 cap;
>  
> +	if (pcie_dpc_disable)
> +		return;
> +

[Severity: High]
Does returning early here leave pdev->dpc_cap as 0 and cause issues with Error
Disconnect Recover (EDR)?

When pci=nodpc is set, calculate_control() in drivers/acpi/pci_root.c still
requests DPC control from firmware based solely on the compile-time flag:

drivers/acpi/pci_root.c:calculate_control() {
    ...
	if (IS_ENABLED(CONFIG_PCIE_DPC) && IS_ENABLED(CONFIG_PCIE_EDR))
		control |= OSC_PCI_EXPRESS_DPC_CONTROL;
    ...
}

And pci_acpi_add_edr_notifier() in drivers/pci/pcie/edr.c unconditionally
enables DPC in hardware:

drivers/pci/pcie/edr.c:pci_acpi_add_edr_notifier() {
    ...
	if (acpi_enable_dpc(pdev))
		acpi_remove_notify_handler(adev->handle, ACPI_SYSTEM_NOTIFY,
					   edr_handle_event);
    ...
}

If a PCIe error occurs and ACPI firmware notifies the OS, edr_handle_event()
will trigger but immediately abort because edev->dpc_cap is 0:

drivers/pci/pcie/edr.c:edr_handle_event() {
    ...
	if (!edev->dpc_cap) {
		pci_err(edev, FW_BUG "This device doesn't support DPC\n");
		goto send_ost;
	}
    ...
}

Will this cause EDR to abort recovery, incorrectly log a firmware bug, and
permanently abandon the link instead of letting userspace handle it?

>  	pdev->dpc_cap = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_DPC);
>  	if (!pdev->dpc_cap)
>  		return;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260709185429.627968-1-yurypm@arista.com?part=2