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Message-ID: <20201124171746.GA565099@bjorn-Precision-5520>
Date: Tue, 24 Nov 2020 11:17:46 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: "Kelley, Sean V" <sean.v.kelley@...el.com>
Cc: "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
"xerces.zhao@...il.com" <xerces.zhao@...il.com>,
"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
"Raj, Ashok" <ashok.raj@...el.com>,
"Luck, Tony" <tony.luck@...el.com>,
"Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>,
"Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
Linux PCI <linux-pci@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 10/15] PCI/ERR: Limit AER resets in pcie_do_recovery()
On Mon, Nov 23, 2020 at 11:57:35PM +0000, Kelley, Sean V wrote:
> > On Nov 23, 2020, at 3:28 PM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> > On Fri, Nov 20, 2020 at 04:10:31PM -0800, Sean V Kelley wrote:
> >> In some cases a bridge may not exist as the hardware controlling may be
> >> handled only by firmware and so is not visible to the OS. This scenario is
> >> also possible in future use cases involving non-native use of RCECs by
> >> firmware.
> >>
> >> Explicitly apply conditional logic around these resets by limiting them to
> >> Root Ports and Downstream Ports.
> >
> > Can you help me understand this? The subject says "Limit AER resets"
> > and here you say "limit them to RPs and DPs", but it's not completely
> > obvious how the resets are being limited, i.e., the patch doesn't add
> > anything like:
> >
> > + if (type == PCI_EXP_TYPE_ROOT_PORT ||
> > + type == PCI_EXP_TYPE_DOWNSTREAM)
> > reset_subordinates(bridge);
> >
> > It *does* add checks around pcie_clear_device_status(), but that also
> > includes RC_EC. And that's not a reset, so I don't think that's
> > explicitly mentioned in the commit log.
>
> The subject should have referred to the clearing of the device status rather than resets.
> It originally came from this simpler patch in which I made use of reset instead of clear:
>
> https://lore.kernel.org/linux-pci/20201002184735.1229220-8-seanvk.dev@oregontracks.org/
>
> So a rephrase of clearing in place of resets would be more appropriate.
>
> Then we added the notion of bridges…below
>
> >
> > Also see the question below.
> >
> >> Link: https://lore.kernel.org/r/20201002184735.1229220-8-seanvk.dev@oregontracks.org
> >> Signed-off-by: Sean V Kelley <sean.v.kelley@...el.com>
> >> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> >> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> >> ---
> >> drivers/pci/pcie/err.c | 31 +++++++++++++++++++++++++------
> >> 1 file changed, 25 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> >> index 8b53aecdb43d..7883c9791562 100644
> >> --- a/drivers/pci/pcie/err.c
> >> +++ b/drivers/pci/pcie/err.c
> >> @@ -148,13 +148,17 @@ static int report_resume(struct pci_dev *dev, void *data)
> >>
> >> /**
> >> * pci_walk_bridge - walk bridges potentially AER affected
> >> - * @bridge: bridge which may be a Port
> >> + * @bridge: bridge which may be a Port, an RCEC with associated RCiEPs,
> >> + * or an RCiEP associated with an RCEC
> >> * @cb: callback to be called for each device found
> >> * @userdata: arbitrary pointer to be passed to callback
> >> *
> >> * If the device provided is a bridge, walk the subordinate bus, including
> >> * any bridged devices on buses under this bus. Call the provided callback
> >> * on each device found.
> >> + *
> >> + * If the device provided has no subordinate bus, call the callback on the
> >> + * device itself.
> >> */
> >> static void pci_walk_bridge(struct pci_dev *bridge,
> >> int (*cb)(struct pci_dev *, void *),
> >> @@ -162,6 +166,8 @@ static void pci_walk_bridge(struct pci_dev *bridge,
> >> {
> >> if (bridge->subordinate)
> >> pci_walk_bus(bridge->subordinate, cb, userdata);
> >> + else
> >> + cb(bridge, userdata);
> >> }
> >>
> >> pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> >> @@ -174,10 +180,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> >>
> >> /*
> >> * Error recovery runs on all subordinates of the bridge. If the
> >> - * bridge detected the error, it is cleared at the end.
> >> + * bridge detected the error, it is cleared at the end. For RCiEPs
> >> + * we should reset just the RCiEP itself.
> >> */
> >> if (type == PCI_EXP_TYPE_ROOT_PORT ||
> >> - type == PCI_EXP_TYPE_DOWNSTREAM)
> >> + type == PCI_EXP_TYPE_DOWNSTREAM ||
> >> + type == PCI_EXP_TYPE_RC_EC ||
> >> + type == PCI_EXP_TYPE_RC_END)
> >> bridge = dev;
> >> else
> >> bridge = pci_upstream_bridge(dev);
> >> @@ -185,6 +194,12 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> >> pci_dbg(bridge, "broadcast error_detected message\n");
> >> if (state == pci_channel_io_frozen) {
> >> pci_walk_bridge(bridge, report_frozen_detected, &status);
> >> + if (type == PCI_EXP_TYPE_RC_END) {
> >> + pci_warn(dev, "subordinate device reset not possible for RCiEP\n");
> >> + status = PCI_ERS_RESULT_NONE;
> >> + goto failed;
> >> + }
> >> +
> >> status = reset_subordinates(bridge);
> >> if (status != PCI_ERS_RESULT_RECOVERED) {
> >> pci_warn(bridge, "subordinate device reset failed\n");
> >> @@ -217,9 +232,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> >> pci_dbg(bridge, "broadcast resume message\n");
> >> pci_walk_bridge(bridge, report_resume, &status);
> >>
> >> - if (pcie_aer_is_native(bridge))
> >> - pcie_clear_device_status(bridge);
> >> - pci_aer_clear_nonfatal_status(bridge);
> >> + if (type == PCI_EXP_TYPE_ROOT_PORT ||
> >> + type == PCI_EXP_TYPE_DOWNSTREAM ||
> >> + type == PCI_EXP_TYPE_RC_EC) {
> >> + if (pcie_aer_is_native(bridge))
> >> + pcie_clear_device_status(bridge);
> >> + pci_aer_clear_nonfatal_status(bridge);
> >
> > This is hard to understand because "type" is from "dev", but "bridge"
> > is not necessarily the same device. Should it be this?
> >
> > type = pci_pcie_type(bridge);
> > if (type == PCI_EXP_TYPE_ROOT_PORT ||
> > ...)
>
> Correct, it would be better if the type was based on the ‘bridge’.
OK. This is similar to
https://lore.kernel.org/linux-pci/20201002184735.1229220-8-seanvk.dev@oregontracks.org/,
which you cited above except for the bridge/dev question and the
addition here of RC_EC.
I tried to split that back into its own patch and started with the
commit message from that patch. But I got stuck on the commit
message. I got as far as:
In some cases an error may be reported by a device not visible to
the OS, e.g., if firmware manages the device and passes error
information to the OS via ACPI APEI.
But I still can't quite connect that to the patch. "bridge" is
clearly a device visible to Linux.
I guess we're trying to assert that if "bridge" is not a Root Port,
Downstream Port, or RCEC, we shouldn't clear the error status because
the error came from a device Linux doesn't know about. But I think
"bridge" is *always* either a Root Port or a Downstream Port:
if (type == PCI_EXP_TYPE_ROOT_PORT ||
type == PCI_EXP_TYPE_DOWNSTREAM)
bridge = dev;
else
bridge = pci_upstream_bridge(dev);
pci_upstream_bridge() returns either NULL (in which case previous uses
dereference a NULL pointer), or dev->bus->self, which is always a Root
Port, Switch Downstream Port, or Switch Upstream Port (or NULL for the
special case of VFs).
> >> + }
> >> pci_info(bridge, "device recovery successful\n");
> >> return status;
> >>
> >> --
> >> 2.29.2
>
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