Previously portdrv tried to prevent non-Root Port (RP) and non-Root
Complex Event Collector (RCEC) devices from enabling AER capability.
This was done because some switches enable AER but do not support MSI.
Hence, trying to initialize the AER IRQ for such devices would fail and
Linux would fail to claim the switch port entirely.

However, it is possible to have switches upstream of an endpoint that
support MSI and AER. Without AER capability being enabled on such
a switch, portdrv will refuse to enable the DPC capability as well,
preventing a PCIe error on an endpoint from being handled by the switch.

Allow enabling the AER service on non-RP, non-RCEC devices if they still
support both AER and MSI. This allows switches upstream of an endpoint
to generate and handle DPC events.
Fixes: d8d2b65a940b ("PCI/portdrv: Allow AER service only for Root Ports & RCECs")
Signed-off-by: Darshit Shah <darnshah@amazon.de>
---
 drivers/pci/pcie/portdrv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
index d1b68c18444f..41326bbcd295 100644
--- a/drivers/pci/pcie/portdrv.c
+++ b/drivers/pci/pcie/portdrv.c
@@ -237,8 +237,8 @@ static int get_port_device_capability(struct pci_dev *dev)
 	}
 
 #ifdef CONFIG_PCIEAER
-	if ((pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
-             pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC) &&
+	if ((dev->msi_cap || pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
+	     pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC) &&
 	    dev->aer_cap && pci_aer_available() &&
 	    (pcie_ports_native || host->native_aer))
 		services |= PCIE_PORT_SERVICE_AER;
-- 
2.47.3




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On Fri, Nov 28, 2025 at 12:20:53PM +0000, Darshit Shah wrote:
> Previously portdrv tried to prevent non-Root Port (RP) and non-Root
> Complex Event Collector (RCEC) devices from enabling AER capability.
> This was done because some switches enable AER but do not support MSI.

The AER driver only binds to RPs and RCECs, see aer_probe():

	if ((pci_pcie_type(port) != PCI_EXP_TYPE_RC_EC) &&
	    (pci_pcie_type(port) != PCI_EXP_TYPE_ROOT_PORT))
		return -ENODEV;

So there's no point in adding PCIE_PORT_SERVICE_AER to "services"
for other port types (as your patch does).

> However, it is possible to have switches upstream of an endpoint that
> support MSI and AER. Without AER capability being enabled on such
> a switch, portdrv will refuse to enable the DPC capability as well,
> preventing a PCIe error on an endpoint from being handled by the switch.

I assume you're referring to this clause in get_port_device_capability():

	if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
	    pci_aer_available() &&
	    (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
		services |= PCIE_PORT_SERVICE_DPC;

Presumably on your system, BIOS doesn't grant AER handling to the OS
upon _OSC negotiation?  Is there a BIOS knob to change that?
Alternatively, does passing "pcie_ports=dpc-native" fix the issue?
If it does, why do you need the patch instead of using the command line
option?

> Allow enabling the AER service on non-RP, non-RCEC devices if they still
> support both AER and MSI. This allows switches upstream of an endpoint
> to generate and handle DPC events.

Per PCIe r7.0 sec 7.8.4.9, regarding the Root Error Command Register:

   "For Functions other than Root Ports and Root Complex Event Collectors:
   when End-End TLP Prefix Supported is Set or Flit Mode Supported is Set,
   this register is RsvdP, otherwise [...] this register is not required
   to be implemented."

Hence we can't enable AER handling on anything else than RPs and RCECs.

Thanks,

Lukas