Re: [PATCH v2] PCI/portdrv: Do not require an interrupt for all AER capable ports

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Dec 07, 2022 at 10:41:05AM +0200, Mika Westerberg wrote:
> Only Root Ports and Event Collectors use MSI for AER. PCIe Switch ports
> or endpoints on the other hand only send messages (that get collected by
> the former). For this reason do not require PCIe switch ports and
> endpoints to use interrupt if they support AER.
> 
> This allows portdrv to attach PCIe switch ports of Intel DG1 and DG2
> discrete graphics cards. These do not declare MSI or legacy interrupts.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Thanks for the additional info!  This seems like something we should
definitely do.

I'm wondering whether we should check for this in
get_port_device_capability().  It already has similar checks for
device type for other services.  This would skip pci_set_master() for
these non-RP, non-RCEC devices, which is probably harmless, since I
assume we only need that to make sure MSI works.

It would also prevent allocation of the AER service for non-RP,
non-RCEC devices.  That's also probably harmless, since aer_probe()
ignores those devices anyway.

What do you think of something like this?  (This is based on my
pci/portdrv branch which squashed everything into portdrv.c:
https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/log/?h=pci/portdrv)

diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
index a6c4225505d5..8b16e96ec15c 100644
--- a/drivers/pci/pcie/portdrv.c
+++ b/drivers/pci/pcie/portdrv.c
@@ -232,7 +232,9 @@ static int get_port_device_capability(struct pci_dev *dev)
 	}
 
 #ifdef CONFIG_PCIEAER
-	if (dev->aer_cap && pci_aer_available() &&
+	if ((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;
 #endif