[PATCH] PCI: Mark Intel bridge on SuperMicro Atom C3xxx motherboards to avoid bus reset

[Maik Broemme <mbroemme@xxxxxxxxxx>]

The Intel PCI bridge on SuperMicro Atom C3xxx motherboards do not
successfully complete a bus reset when used with certain child devices.
After the reset, config accesses to the child may fail. If assigning
such device via VFIO it will immediately fail with:

  vfio-pci 0000:01:00.0: Failed to return from FLR
  vfio-pci 0000:01:00.0: timed out waiting for pending transaction;
  performing function level reset anyway

Device will disappear from PCI device list:

  !!! Unknown header type 7f
  Kernel driver in use: vfio-pci
  Kernel modules: ddbridge

The attached patch will mark the root port as incapable of doing a
bus level reset. After that all my tested devices survive a VFIO
assignment and several VM reboot cycles.

Signed-off-by: Maik Broemme <mbroemme@xxxxxxxxxx>
---
 drivers/pci/quirks.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 0f16acc323c6..86cd42872708 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -3433,6 +3433,13 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0034, quirk_no_bus_reset);
  */
 DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_CAVIUM, 0xa100, quirk_no_bus_reset);
 
+/*
+ * Root port on some SuperMicro Atom C3xxx motherboards do not successfully
+ * complete a bus reset when used with certain child devices. After the
+ * reset, config accesses to the child may fail.
+ */
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x19a4, quirk_no_bus_reset);
+
 static void quirk_no_pm_reset(struct pci_dev *dev)
 {
 	/*
-- 
2.21.0