Re: [PATCH v2] PCI/portdrv: Allow probing even without child services

[Bjorn Helgaas]

On Fri, Jul 17, 2026 at 10:26:53AM +0200, Lukas Wunner wrote:
> On Thu, Jul 16, 2026 at 12:26:41PM -0500, Bjorn Helgaas wrote:
> > On Mon, Feb 09, 2026 at 05:15:35PM -0800, 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 have no
> > > PCIe capabilities, 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 have 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, thank you!
> 
> Some thoughts on the version now applied to pci/portdrv:
> 
> * After this patch, the return value of pcie_device_init() is no longer
>   evaluated, so that function should be changed to return void as part
>   of this patch.
> 
> * If no port services are initalized, e.g. because pcie_device_init()
>   failed for all of them, the allocated IRQ vectors are not freed.
>   They're hogged, which may be a problem on systems which only support
>   very few IRQ vectors such as Sophgo SG2042:
> 
>   https://lore.kernel.org/r/0f42afefd9322779af5463b696c55b08d2296ea8.camel@xxxxxxxxxxx

Seems like a good idea to free IRQ vectors we don't use.  It *looks*
like it should be safe to call pci_free_irq_vectors() here and then
again in pcie_port_device_remove() if a port is removed, but Brian
wasn't sure, and I didn't look any deeper than pci_disable_msix() and
pci_disable_msi().

I guess if we did this we'd need to retain the pcie_device_init().

> * It might be clearer to call pci_clear_master() directly in the
>   if-block which is amended to "goto out".  Then the "goto out"
>   can be changed to a "return 0".  It seems "if (!capabilities)"
>   cannot happen through any other code path, so it's unclear why
>   the "out" label is necessary.

It does look nicer that way.

> * There's a duplicate "have" in the commit message ("have only have").

I fixed this on pci/portdrv.

What do you think, Brian?