[PATCH v2 1/2] PCI/ERR: Fix fatal error recovery for non-hotplug capable devices

[sathyanarayanan.kuppuswamy@linux.intel.com]

From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Fatal (DPC) error recovery is currently broken for non-hotplug
capable devices. With current implementation, after successful
fatal error recovery, non-hotplug capable device state won't be
restored properly. You can find related issues in following links.

https://lkml.org/lkml/2020/5/27/290
https://lore.kernel.org/linux-pci/12115.1588207324@famine/
https://lkml.org/lkml/2020/3/28/328

Current fatal error recovery implementation relies on hotplug handler
for detaching/re-enumerating the affected devices/drivers on DLLSC
state changes. So when dealing with non-hotplug capable devices,
recovery code does not restore the state of the affected devices
correctly. Correct implementation should call report_slot_reset()
function after resetting the link to restore the state of the
device/driver.

So use PCI_ERS_RESULT_NEED_RESET as error status for successful
reset_link() operation and use PCI_ERS_RESULT_DISCONNECT for failure
case. PCI_ERS_RESULT_NEED_RESET error state will ensure slot_reset()
is called after reset link operation which will also fix the above
mentioned issue.

[original patch is from jay.vosburgh@canonical.com]
[original patch link https://lore.kernel.org/linux-pci/12115.1588207324@famine/]
Fixes: 6d2c89441571 ("PCI/ERR: Update error status after reset_link()")
Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
 drivers/pci/pcie/err.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 14bb8f54723e..5fe8561c7185 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -165,8 +165,28 @@ 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_bus(bus, report_frozen_detected, &status);
-		status = reset_link(dev);
-		if (status != PCI_ERS_RESULT_RECOVERED) {
+		/*
+		 * After resetting the link using reset_link() call, the
+		 * possible value of error status is either
+		 * PCI_ERS_RESULT_DISCONNECT (failure case) or
+		 * PCI_ERS_RESULT_NEED_RESET (success case).
+		 * So ignore the return value of report_error_detected()
+		 * call for fatal errors. Instead use
+		 * PCI_ERS_RESULT_NEED_RESET as initial status value.
+		 *
+		 * Ignoring the status return value of report_error_detected()
+		 * call will also help in case of EDR mode based error
+		 * recovery. In EDR mode AER and DPC Capabilities are owned by
+		 * firmware and hence report_error_detected() call will possibly
+		 * return PCI_ERS_RESULT_NO_AER_DRIVER. So if we don't ignore
+		 * the return value of report_error_detected() then
+		 * pcie_do_recovery() would report incorrect status after
+		 * successful recovery. Ignoring PCI_ERS_RESULT_NO_AER_DRIVER
+		 * in non EDR case should not have any functional impact.
+		 */
+		status = PCI_ERS_RESULT_NEED_RESET;
+		if (reset_link(dev) != PCI_ERS_RESULT_RECOVERED) {
+			status = PCI_ERS_RESULT_DISCONNECT;
 			pci_warn(dev, "link reset failed\n");
 			goto failed;
 		}
-- 
2.17.1