linux-kernel - Re: [PATCH 1/5] PCI/DPC: Ignore devices with no AER Capability

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Date:   Wed, 25 Nov 2020 18:01:57 -0800
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     ashok.raj@...el.com, knsathya@...nel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH 1/5] PCI/DPC: Ignore devices with no AER Capability



On 11/25/20 5:18 PM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> Downstream Ports may support DPC regardless of whether they support AER
> (see PCIe r5.0, sec 6.2.10.2).  Previously, if the user booted with
> "pcie_ports=dpc-native", it was possible for dpc_probe() to succeed even if
> the device had no AER Capability, but dpc_get_aer_uncorrect_severity()
> depends on the AER Capability.
> 
> dpc_probe() previously failed if:
> 
>    !pcie_aer_is_native(pdev) && !pcie_ports_dpc_native
>    !(pcie_aer_is_native() || pcie_ports_dpc_native)    # by De Morgan's law
> 
> so it succeeded if:
> 
>    pcie_aer_is_native() || pcie_ports_dpc_native
> 
> Fail dpc_probe() if the device has no AER Capability.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Olof Johansson <olof@...om.net>
> ---
>   drivers/pci/pcie/dpc.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> index e05aba86a317..ed0dbc43d018 100644
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
> @@ -287,6 +287,9 @@ static int dpc_probe(struct pcie_device *dev)
>   	int status;
>   	u16 ctl, cap;
>   
> +	if (!pdev->aer_cap)
> +		return -ENOTSUPP;
Don't we check aer_cap support in drivers/pci/pcie/portdrv_core.c ?

We don't enable DPC service, if AER service is not enabled. And AER
service is only enabled if AER capability is supported.

So dpc_probe() should not happen if AER capability is not supported?

206 static int get_port_device_capability(struct pci_dev *dev)
...
...
251         if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
252             host->native_dpc &&
253             (host->native_dpc || (services & PCIE_PORT_SERVICE_AER)))
254                 services |= PCIE_PORT_SERVICE_DPC;
255

> +
>   	if (!pcie_aer_is_native(pdev) && !pcie_ports_dpc_native)
>   		return -ENOTSUPP;
>   
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer