linux-kernel - Re: [PATCH v3] PCI/portdrv: Allow AER service only for Root Ports & RCECs

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Date: Thu, 14 Dec 2023 14:28:56 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Matthew W Carlis <mattc@...estorage.com>
Cc: bhelgaas@...gle.com, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, mika.westerberg@...ux.intel.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v3] PCI/portdrv: Allow AER service only for Root Ports &
 RCECs

On Wed, Dec 13, 2023 at 11:37:17PM -0700, Matthew W Carlis wrote:
> Hello Any Interested
> 
> Recently found that this patch had the affect of requiring us to set
> pcie_ports_dpc_native in order to use the kernel DPC driver with PCIe switch
> downstream ports. The kernel check for the DPC capability in portdrv.c has;
> if pci_aer_available() and (dpc-native or using AER port service driver on
> the device). I wonder if we couldn't do away with the requirement of the
> AER service being used on the port if pci_aer_available() & host->native_aer
> don't lie. I'm still trying to decide exactly what the condition ought to
> look like, but it might draw from the AER service check above it. For example:
> 
>         if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
> -           pci_aer_available() &&
> -           (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
> +           dev->aer_cap && pci_aer_available() &&
> +           (pcie_ports_dpc_native || host->native_aer))
>                 services |= PCIE_PORT_SERVICE_DPC;

This sounds like it might be a regression report for d8d2b65a940b
("PCI/portdrv: Allow AER service only for Root Ports & RCECs"), which
appeared in v6.2.  Is that true?

If d8d2b65a940b requires you to use the "pcie_ports=dpc-native" kernel
parameter when you didn't need it before, that sounds like a
regression.

Looking at the code, that "services & PCIE_PORT_SERVICE_AER"
definitely looks like a problem.  We added that with 
https://git.kernel.org/linus/4e5fad429bd1 ("PCI/DPC: Do not enable DPC
if AER control is not allowed by the BIOS"), but I think your
suggestion of checking host->native_aer is better.

Do you want to post a formal patch for it?

Bjorn