[PATCH v2] PCI/AER: Add support for reset of RCiEPs for APEI/Firmware first reporting only

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

Was previously: PCI/AER: Add partial initial supprot for RCiEPs using RCEC or
firmware first.

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.

This code will only perform the correct reset flow for the case where 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.

As there is no current RCEC driver support, it should not be possible to get
to this code via any routes other than the one above. Hence appropriate RCEC
handling can be added when the RCEC driver support is ready.

The error handling is different from a normal PCIe End Point because:

1) There is no downstream port above an RCiEP as these devices sit on a root
   bus.

2) In general, it makes little sense to reset other devices on on the same
   root bus.  For error handling outside the of the root complex (RC) an AER
   error will indicate that all the topology below the physical link, which
   the error is related to, will need to be reset as they share a common
   path to the host.  For an RCiEP there is no such defined shared path
   relationship with other elements on the root bus.

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.   This function allows us to
avoid adding special cases to the majority of the error handling.

Open questions:

1. Are we better protecting against link reset for an RCiEP in here or
   should we put the check in the link reset functions?

2. If we were to get a stupid firmware record with the relevant reset flag
   set to trigger a link reset, what is the correct response?  For now I
   try to report that we haven't done anything and print a warning.

3. Naming of pci_walk_below_dev is rather unsatisfying. Any better ideas?

4. pci_walk_below_dev is perhaps not of general utility. Shall I make it local
   in err.c?  If not would a precursor patch for that be preferred?

Testing has been performed via error injection on a QEMU platform as that lets
me create a wide range of topologies and report errors at any chosen location.
Currently I have no plans to upstream this injection support, but am happy to
share if useful to others.

[0] ACPI PCI Express Base Specification 4.0 1.3.2.3 Root Complex Integrated
    Endpoint Rules.
[1] ACPI PCI Express Base Specification 4.0 6.2 Error Signalling and Logging
[2] ACPI Specification 6.3 Chapter 18 ACPI Platform Error Interface (APEI)
[3] ACPI Sepcification 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@huawei.com>
---
Changes since v1:
* Separated from the largely unrelated fix so the two can move forwards separately.
* Instead of separate path for RCiEP handling use the method suggested by Bjorn
  and Sathyanarayanan with an adjusted pci_bus_walk.

Thanks all for reviews of V1.
  
 drivers/pci/bus.c      | 28 ++++++++++++++++++++++++++++
 drivers/pci/pcie/err.c | 29 +++++++++++++++++++----------
 include/linux/pci.h    |  2 ++
 3 files changed, 49 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 8e40b3e6da77..7cbe1ed2db3d 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -411,6 +411,34 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
 }
 EXPORT_SYMBOL_GPL(pci_walk_bus);
 
+/** pci_walk_below_dev - walk devices below (or on) another device
+ *  @dev      device for which we should walk below, include device when not 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 hs no subordinate bus, call the provided
+ *  callback on the device itself.
+ *
+ */
+void pci_walk_below_dev(struct pci_dev *dev, int (*cb)(struct pci_dev *, void *),
+			void *userdata)
+{
+	struct pci_bus *bus;
+
+	if (dev->subordinate) {
+		bus = dev->subordinate;
+		pci_walk_bus(bus, cb, userdata);
+	} else {
+		cb(dev, userdata);
+	}
+}
+EXPORT_SYMBOL_GPL(pci_walk_below_dev);
+
 struct pci_bus *pci_bus_get(struct pci_bus *bus)
 {
 	if (bus)
diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 14bb8f54723e..fa08b1cc3d96 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -151,33 +151,39 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
 			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))
 		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_below_dev(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");
+			status = PCI_ERS_RESULT_NONE;
+			goto failed;
+		}
+
 		status = reset_link(dev);
 		if (status != PCI_ERS_RESULT_RECOVERED) {
 			pci_warn(dev, "link reset failed\n");
 			goto failed;
 		}
 	} else {
-		pci_walk_bus(bus, report_normal_detected, &status);
+		pci_walk_below_dev(dev, report_normal_detected, &status);
 	}
 
 	if (status == PCI_ERS_RESULT_CAN_RECOVER) {
 		status = PCI_ERS_RESULT_RECOVERED;
 		pci_dbg(dev, "broadcast mmio_enabled message\n");
-		pci_walk_bus(bus, report_mmio_enabled, &status);
+		pci_walk_below_dev(dev, report_mmio_enabled, &status);
 	}
 
 	if (status == PCI_ERS_RESULT_NEED_RESET) {
@@ -188,17 +194,20 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
 		 */
 		status = PCI_ERS_RESULT_RECOVERED;
 		pci_dbg(dev, "broadcast slot_reset message\n");
-		pci_walk_bus(bus, report_slot_reset, &status);
+		pci_walk_below_dev(dev, report_slot_reset, &status);
 	}
 
 	if (status != PCI_ERS_RESULT_RECOVERED)
 		goto failed;
 
 	pci_dbg(dev, "broadcast resume message\n");
-	pci_walk_bus(bus, report_resume, &status);
+	pci_walk_below_dev(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_aer_clear_device_status(dev);
+		pci_aer_clear_nonfatal_status(dev);
+	}
 	pci_info(dev, "device recovery successful\n");
 	return status;
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index c79d83304e52..538bf0a76d33 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1411,6 +1411,8 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
 
 void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
 		  void *userdata);
+void pci_walk_below_dev(struct pci_dev *dev, int (*cb)(struct pci_dev *, void *),
+			void *userdata);
 int pci_cfg_space_size(struct pci_dev *dev);
 unsigned char pci_bus_max_busnr(struct pci_bus *bus);
 void pci_setup_bridge(struct pci_bus *bus);
-- 
2.19.1