[PATCH v7 4/5] PCI: 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 simplify 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>
Tested-by: Wen Jin <wen.jin@intel.com>
Tested-by: Shanshan Zhang <ShanshanX.Zhang@intel.com>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.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.

 drivers/pci/pci.h | 53 ++++++++++++++++++-----------------------------
 1 file changed, 20 insertions(+), 33 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 455b32187abd..47af1ff2a286 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -354,44 +354,31 @@ struct pci_sriov {
  *
  * Must be called with device_lock held.
  *
- * Returns true if state has been changed to the requested state.
+ * Returns true if state has been really changed to the requested state.
  */
 static inline bool pci_dev_set_io_state(struct pci_dev *dev,
 					pci_channel_state_t new)
 {
-	bool changed = false;
-
 	device_lock_assert(&dev->dev);
-	switch (new) {
-	case pci_channel_io_perm_failure:
-		switch (dev->error_state) {
-		case pci_channel_io_frozen:
-		case pci_channel_io_normal:
-		case pci_channel_io_perm_failure:
-			changed = true;
-			break;
-		}
-		break;
-	case pci_channel_io_frozen:
-		switch (dev->error_state) {
-		case pci_channel_io_frozen:
-		case pci_channel_io_normal:
-			changed = true;
-			break;
-		}
-		break;
-	case pci_channel_io_normal:
-		switch (dev->error_state) {
-		case pci_channel_io_frozen:
-		case pci_channel_io_normal:
-			changed = true;
-			break;
-		}
-		break;
-	}
-	if (changed)
-		dev->error_state = new;
-	return changed;
+
+/*
+ *			Truth table:
+ *			requested new state
+ *     current          ------------------------------------------
+ *     state            normal         frozen         perm_failure
+ *     ------------  +  -------------  -------------  ------------
+ *     normal        |  normal         frozen         perm_failure
+ *     frozen        |  normal         frozen         perm_failure
+ *     perm_failure  |  perm_failure*  perm_failure*  perm_failure
+ */
+
+	if (dev->error_state == pci_channel_io_perm_failure)
+		return false;
+	else if (dev->error_state == new)
+		return false;
+
+	dev->error_state = new;
+	return true;
 }
 
 static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
-- 
2.18.4