Re: [PATCH v4] PCI/portdrv: Allow probing even without child services

[Bjorn Helgaas]

On Wed, Jul 22, 2026 at 04:09:42PM -0700, Brian Norris wrote:
> The PCIe port driver fails to probe if it finds no child services,
> presumably under the assumption that the driver is not useful in that case.
> However, the driver *can* still be useful for power management support --
> namely, it still configures the port for runtime PM / D3, which may be
> important for allowing a bridge to enter low power modes.
> 
> Thus, allow probe to succeed even if no IRQs and no child services are
> available. This also mirrors existing behavior for ports that don't support
> any portdrv services (PCIe hotplug, AER, DPC, PME, bwctrl), where we'd also
> probe successfully.
> 
> This change is a bit more important after commit f5cd8a929c82 ("PCI: dwc:
> Remove MSI/MSIX capability for Root Port if iMSI-RX is used as MSI
> controller"), because it's common for some DWC-based systems to:
> 
>   1. have only the "aer" and "pcie_pme" port services available and
> 
>   2. not define legacy INTx interrupts properly in their device tree.
> 
> After commit f5cd8a929c82, such systems may fail pcie_init_service_irqs()
> and so exit with -ENODEV.
> 
> Link: https://lore.kernel.org/all/nyada24tqwlkzdceyoxbzitzygvp4elvj5oajnqdwb33xkcdwk@76vnrx45fsfd/
> Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>

Applied to pci/portdrv for v7.3, thanks!

> ---
> 
> Changes in v4:
>  * Between sashiko-bot / Mani / me / Bjorn, we agreed that deferring
>    pci_set_master() may cause us to drop some MSIs:
>      https://lore.kernel.org/all/af574zaysKnXjx15@xxxxxxxxxx/
>    So we revert to the v2 approach, with some small changes
>  * Address some of Lukas's review comments:
>      https://lore.kernel.org/all/al68lFtbq_Q4RCL2@xxxxxxxxxx/
>    Specifically:
>      - ensure pcie_device_init() return code is checked
>      - release IRQs (pci_free_irq_vectors()) when no services registered
>        properly
>  * Borrow some of Bjorn's commit message tweaks
> 
> Changes in v3:
>  * Defer pci_set_master() until we really know we have some child
>    service
> 
> Changes in v2:
>  * Clear master when we have no child services
> 
>  drivers/pci/pcie/portdrv.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
> index 2d6aa488fe7b..18ee190acc6e 100644
> --- a/drivers/pci/pcie/portdrv.c
> +++ b/drivers/pci/pcie/portdrv.c
> @@ -330,7 +330,7 @@ static int pcie_device_init(struct pci_dev *pdev, int service, int irq)
>   */
>  static int pcie_port_device_register(struct pci_dev *dev)
>  {
> -	int status, capabilities, i, nr_service;
> +	int status, capabilities, i;
>  	int irqs[PCIE_PORT_DEVICE_MAXSERVICES];
>  
>  	/* Enable PCI Express port device */
> @@ -355,29 +355,29 @@ static int pcie_port_device_register(struct pci_dev *dev)
>  	if (status) {
>  		capabilities &= PCIE_PORT_SERVICE_HP;
>  		if (!capabilities)
> -			goto error_disable;
> +			goto out;
>  	}
>  
>  	/* Allocate child services if any */
> -	status = -ENODEV;
> -	nr_service = 0;
>  	for (i = 0; i < PCIE_PORT_DEVICE_MAXSERVICES; i++) {
>  		int service = 1 << i;
>  		if (!(capabilities & service))
>  			continue;
> -		if (!pcie_device_init(dev, service, irqs[i]))
> -			nr_service++;
> +		if (pcie_device_init(dev, service, irqs[i]))
> +			capabilities &= ~service;
>  	}
> -	if (!nr_service)
> -		goto error_cleanup_irqs;
>  
> -	return 0;
> +out:
> +	/*
> +	 * With no child services, we shouldn't need bus mastering or any IRQ
> +	 * vectors we allocated.
> +	 */
> +	if (!capabilities) {
> +		pci_free_irq_vectors(dev);
> +		pci_clear_master(dev);
> +	}
>  
> -error_cleanup_irqs:
> -	pci_free_irq_vectors(dev);
> -error_disable:
> -	pci_disable_device(dev);
> -	return status;
> +	return 0;
>  }
>  
>  typedef int (*pcie_callback_t)(struct pcie_device *);
> -- 
> 2.55.0.229.g6434b31f56-goog
>