Re: [PATCH v8 08/14] PCI/AER: Extend AER error handling to RCECs

From: Sean V Kelley
Date: Fri Oct 09 2020 - 17:54:47 EST

On 9 Oct 2020, at 14:27, Bjorn Helgaas wrote:

On Fri, Oct 02, 2020 at 11:47:29AM -0700, Sean V Kelley wrote:
From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

Currently the kernel does not handle AER errors for Root Complex
integrated End Points (RCiEPs)[0]. These devices sit on a root bus within
the Root Complex (RC). AER handling is performed by a Root Complex Event
Collector (RCEC) [1] which is a effectively a type of RCiEP on the same
root bus.

For an RCEC (technically not a Bridge), error messages "received" from
associated RCiEPs must be enabled for "transmission" in order to cause a
System Error via the Root Control register or (when the Advanced Error
Reporting Capability is present) reporting via the Root Error Command
register and logging in the Root Error Status register and Error Source
Identification register.

In addition to the defined OS level handling of the reset flow for the
associated RCiEPs of an RCEC, it is possible to also have non-native
handling. In that case there is no need to take any actions on the RCEC
because the firmware is responsible for them. This is true where APEI [2]
is used to report the AER errors via a GHES[v2] HEST entry [3] and
relevant AER CPER record [4] and non-native handling is in use.

We effectively end up with two different types of discovery for
purposes of handling AER errors:

1) Normal bus walk - we pass the downstream port above a bus to which
the device is attached and it walks everything below that point.

2) An RCiEP with no visible association with an RCEC as there is no need
to walk devices. In that case, the flow is to just call the callbacks for
the actual device, which in turn references its associated RCEC.

Modify pci_walk_bridge() to handle devices which lack a subordinate bus.
If the device does not then it will call the function on that device
alone.

[0] ACPI PCI Express Base Specification 5.0-1 1.3.2.3 Root Complex
Integrated Endpoint Rules.
[1] ACPI PCI Express Base Specification 5.0-1 6.2 Error Signalling and
Logging
[2] ACPI Specification 6.3 Chapter 18 ACPI Platform Error Interface (APEI)
[3] ACPI Specification 6.3 18.2.3.7 Generic Hardware Error Source
[4] UEFI Specification 2.8, N.2.7 PCI Express Error Section

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: Sean V Kelley <sean.v.kelley@xxxxxxxxx>
---
drivers/pci/pcie/err.c | 25 ++++++++++++++++++++-----
1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 5ff1afa4763d..c4ceca42a3bf 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -148,19 +148,25 @@ 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 an RCEC with associated RCiEPs,
+ * an RCiEP associated with an RCEC, or a Port.
* @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 provided
+ * callback on the device itself.
*/
static void pci_walk_bridge(struct pci_dev *bridge, int (*cb)(struct pci_dev *, void *),
void *userdata)
{
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,
@@ -174,11 +180,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
/*
* Error recovery runs on all subordinates of the first downstream
* bridge. If the downstream bridge detected the error, it is
- * cleared at the end.
+ * cleared at the end. For RCiEPs we should reset just the RCiEP itself.
*/
type = pci_pcie_type(dev);
if (type == PCI_EXP_TYPE_ROOT_PORT ||
- type == PCI_EXP_TYPE_DOWNSTREAM)
+ type == PCI_EXP_TYPE_DOWNSTREAM ||
+ type == PCI_EXP_TYPE_RC_EC ||

What is the case where an RCEC is passed to pcie_do_recovery()? I
guess it's the case where an RCEC is reporting an error that it logged
itself, i.e., no RCiEP is involved at all? In that case I guess we
should try an FLR on the RCEC and clear its status?

(I don't think the current series attempts the FLR.)

Correct, we can get errors reported by that same RCEC that are not
related to the associated RCiEPs. Further, an RCiEP in reporting an
error will trigger logging to the Root Error Command/Status and Error
Source Identification registers of the associated RCEC. The assumption
in pcie_do_recovery() here is that I can cover both scenarios.

We could attempt an FLR on the RCEC itself as well.



+ type == PCI_EXP_TYPE_RC_END)
bridge = dev;
else
bridge = pci_upstream_bridge(dev);
@@ -186,7 +194,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
pci_dbg(dev, "broadcast error_detected message\n");
if (state == pci_channel_io_frozen) {
pci_walk_bridge(bridge, report_frozen_detected, &status);
- status = reset_subordinate_device(bridge);
+ 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_subordinate_devices(bridge);
if (status != PCI_ERS_RESULT_RECOVERED) {
pci_warn(dev, "subordinate device reset failed\n");
goto failed;
@@ -219,7 +233,8 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
pci_walk_bridge(bridge, report_resume, &status);

if (type == PCI_EXP_TYPE_ROOT_PORT ||
- type == PCI_EXP_TYPE_DOWNSTREAM) {
+ 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);
--
2.28.0