linux-kernel - Re: [PATCH] drivers/pci: Allow attaching AER to non-RP devices that support MSI

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Message-ID: <20251209003003.GA3436550@bhelgaas>
Date: Mon, 8 Dec 2025 18:30:03 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Darshit Shah <darnshah@...zon.de>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Lukas Wunner <lukas@...ner.de>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Jonathan Cameron <Jonthan.Cameron@...wei.com>, darnir@....org,
	Feng Tang <feng.tang@...ux.alibaba.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, nh-open-source@...zon.com
Subject: Re: [PATCH] drivers/pci: Allow attaching AER to non-RP devices that
 support MSI

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.
> Hence, trying to initialize the AER IRQ for such devices would fail and
> Linux would fail to claim the switch port entirely.

The d8d2b65a940b commit log could have been clearer.

Some switches advertise an AER capability, but they can't generate AER
interrupts, regardless of whether they support MSI.  Only RPs and
RCECs can generate AER interrupts.

> 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@...zon.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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