[PATCH v8 5/6] PCI/ERR: only return true when dev io state is really changed

[Ethan Zhao <haifeng.zhao@intel.com>]

When uncorrectable error happens, AER driver and DPC driver interrupt
handlers likely call

   pcie_do_recovery()
   ->pci_walk_bus()
     ->report_frozen_detected()

with pci_channel_io_frozen the same time.
   If pci_dev_set_io_state() return true even if the original state is
pci_channel_io_frozen, that will cause AER or DPC handler re-enter
the error detecting and recovery procedure one after another.
   The result is the recovery flow mixed between AER and DPC.
So change the pci_dev_set_io_state() function to only return true
when dev->error_state is really changed.

Signed-off-by: Ethan Zhao <haifeng.zhao@intel.com>
---
Changnes:
 v2: revise description and code according to suggestion from Andy.
 v3: change code to simpler.
 v4: no change.
 v5: no change.
 v6: no change.
 v7: changed based on Bjorn's code and truth table.
 v8: according to Bjorn's suggestion, rebase on another simplification
     patch.   

 drivers/pci/pci.h | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index bceb3f108744..a11e0f9d9bdf 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -371,17 +371,14 @@ static inline bool pci_dev_set_io_state(struct pci_dev *dev,
  *     perm_failure  |  perm_failure*  perm_failure*  perm_failure
  */
 
-	/* Can always put a device in perm_failure state */
-	if (new == pci_channel_io_perm_failure) {
-		dev->error_state = pci_channel_io_perm_failure;
-		return true;
-	}
-
-	/* If already in perm_failure, can't set to normal or frozen */
+	/* If already in perm_failure, can't change it's state */
 	if (dev->error_state == pci_channel_io_perm_failure)
 		return false;
+	/* not change at all */
+	else if (dev->error_state == new)
+		return false;
 
-	 /* Can always change normal to frozen or vice versa */
+	 /* Can always change from normal/frozen to other different state */
 	dev->error_state = new;
 	return true;
 }
-- 
2.18.4