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

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Message-ID: <20201128232500.GA929114@bjorn-Precision-5520>
Date:   Sat, 28 Nov 2020 17:25:00 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
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 Sat, Nov 28, 2020 at 01:56:23PM -0800, Kuppuswamy, Sathyanarayanan wrote:
> On 11/28/20 1:53 PM, Bjorn Helgaas wrote:
> > 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@...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?
> > > > 
> > > > 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.

> In that case, can you move this check to
> drivers/pci/pcie/portdrv_core.c?  I don't see the point of
> distributed checks in both get_port_device_capability() and
> dpc_probe().

I totally agree that these distributed checks are terrible, but my
long-term hope is to get rid of portdrv and handle these "services"
more like we handle other capabilities.  For example, maybe we can
squash dpc_probe() into pci_dpc_init(), so I'd actually like to move
things from get_port_device_capability() into dpc_probe().