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    SubjectRe: [PATCH 1/5] PCI/DPC: Ignore devices with no AER Capability
    On Sat, Nov 28, 2020 at 01:49:46PM -0800, Kuppuswamy, Sathyanarayanan wrote:
    > On 11/28/20 12:24 PM, Bjorn Helgaas wrote:
    > > On Wed, Nov 25, 2020 at 06:01:57PM -0800, Kuppuswamy, Sathyanarayanan wrote:
    > > > On 11/25/20 5:18 PM, Bjorn Helgaas wrote:
    > > > > From: Bjorn Helgaas <bhelgaas@google.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@google.com>
    > > > > Cc: Olof Johansson <olof@lixom.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?
    > >
    > > I don't think that's always true. If I'm reading this right, we have
    > > this:
    > >
    > > get_port_device_capability(...)
    > > {
    > > #ifdef CONFIG_PCIEAER
    > > if (dev->aer_cap && ...)
    > > services |= PCIE_PORT_SERVICE_AER;
    > > #endif
    > >
    > > 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;
    > > }
    > >
    > > and in the case where:
    > >
    > > - CONFIG_PCIEAER=y
    > > - booted with "pcie_ports=dpc-native" (pcie_ports_dpc_native is true)
    > > - "dev" has no AER capability
    > > - "dev" has DPC capability
    > >
    > > I think we do enable PCIE_PORT_SERVICE_DPC.
    > Got it. But further looking into it, I am wondering whether
    > we should keep this dependency? Currently we just use it to
    > dump the error information. Do we need to create dependency
    > between DPC and AER (which is functionality not dependent) just
    > to see more details about the error?

    That's a good question, but I don't really want to get into the actual
    operation of the AER and DPC drivers in this series, so maybe
    something we should explore later.

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