Re: [RFC PATCH 4/9] PCI/AER: Extend AER error handling to RCECs

From: Sean V Kelley
Date: Mon Jul 27 2020 - 10:59:06 EST

On 27 Jul 2020, at 4:00, Jonathan Cameron wrote:

On Fri, 24 Jul 2020 10:22:18 -0700
Sean V Kelley <sean.v.kelley@xxxxxxxxx> 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 a firmware first
model. 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 Firmware First 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

A new walk function, similar to pci_bus_walk is provided that takes a pci_dev
instead of a bus. If that dev corresponds to a downstream port it will walk
the subordinate bus of that downstream port. If the dev does not then it
will call the function on that device alone.

[0] ACPI PCI Express Base Specification 5.0-1 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 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>
Changes since v2 [1]:

- Renamed to pci_walk_dev_affected() to reflect the aer affected devices
Make sense.

- Localized to err.c and made static

Makes sense.

- Added check for RCEC to reflect
That comment probably needs a bit more...

Will add to the details.

- Tightened up commit log from earlier inquiry focused RFC

Looks good to me and I like the new naming.

A few really trivial tidy ups suggested for things that were less than neat in my patch.


drivers/pci/pcie/err.c | 55 ++++++++++++++++++++++++++++++++++--------
1 file changed, 45 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 14bb8f54723e..044df004f20b 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -146,38 +146,69 @@ static int report_resume(struct pci_dev *dev, void *data)
return 0;

+/** pci_walk_dev_affected - walk devices potentially AER affected
* pci_walk_dev_affected

There is a bit of a mixture in pci files between the two styles, but
I'm fairly sure kernel-doc is supposed to be as I'm suggesting
(I had this wrong due to cut and paste in earlier version!)

Will fix.

+ * @dev device 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 port, 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.
+ *

I also had an ugly pointless newline here. oops :)

Will fix.



+ */
+static void pci_walk_dev_affected(struct pci_dev *dev, int (*cb)(struct pci_dev *, void *),
+ void *userdata)
+ if (dev->subordinate) {
+ pci_walk_bus(dev->subordinate, cb, userdata);
+ } else {
+ cb(dev, userdata);
+ }
pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
enum pci_channel_state state,
pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
- struct pci_bus *bus;

* Error recovery runs on all subordinates of the first downstream port.
* If the downstream port detected the error, it is cleared at the end.
+ * For RCiEPs we should reset just the RCiEP itself.
if (!(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
- pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM))
+ pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
+ pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END ||
+ pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC))
dev = dev->bus->self;
- bus = dev->subordinate;

pci_dbg(dev, "broadcast error_detected message\n");
if (state == pci_channel_io_frozen) {
- pci_walk_bus(bus, report_frozen_detected, &status);
+ pci_walk_dev_affected(dev, report_frozen_detected, &status);
+ if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
+ pci_warn(dev, "link reset not possible for RCiEP\n");
+ goto failed;
+ }
status = reset_link(dev);
pci_warn(dev, "link reset failed\n");
goto failed;
} else {
- pci_walk_bus(bus, report_normal_detected, &status);
+ pci_walk_dev_affected(dev, report_normal_detected, &status);

pci_dbg(dev, "broadcast mmio_enabled message\n");
- pci_walk_bus(bus, report_mmio_enabled, &status);
+ pci_walk_dev_affected(dev, report_mmio_enabled, &status);

if (status == PCI_ERS_RESULT_NEED_RESET) {
@@ -188,17 +219,21 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
pci_dbg(dev, "broadcast slot_reset message\n");
- pci_walk_bus(bus, report_slot_reset, &status);
+ pci_walk_dev_affected(dev, report_slot_reset, &status);

goto failed;

pci_dbg(dev, "broadcast resume message\n");
- pci_walk_bus(bus, report_resume, &status);
+ pci_walk_dev_affected(dev, report_resume, &status);

- pci_aer_clear_device_status(dev);
- pci_aer_clear_nonfatal_status(dev);
+ if ((pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
+ pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
+ pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC)) {
+ pci_aer_clear_device_status(dev);
+ pci_aer_clear_nonfatal_status(dev);
+ }
pci_info(dev, "device recovery successful\n");
return status;