The PM control register is not accessible in D3cold so we shouldn't try
writing to it in pci_raw_set_power_state() and return an error instead.

The current behaviour is fatal for devices which are not power-managed
by the platform, yet can be runtime suspended to D3cold with some other
mechanism by the driver:

- When the device is runtime resumed, pci_pm_runtime_resume() first
  calls pci_restore_standard_config() which calls pci_set_power_state()
  which calls pci_raw_set_power_state() to put the device into D0.
  This fails since the device is still in D3cold.  It will be powered up
  later on when pci_pm_runtime_resume() calls the driver's
  ->runtime_resume callback.

- pci_raw_set_power_state() prints a message that the device refused to
  change power state and returns 0.  Further up in the call stack,
  pci_restore_standard_config() calls pci_restore_state(), which fails
  since the device is in D3cold, but nevertheless invalidates the
  saved_state.

- When pci_pm_runtime_resume() finally calls the driver ->runtime_resume
  callback to power up the device, the saved_state is gone.

Return an error from pci_raw_set_power_state() to avoid this.

An example for devices affected by this are Thunderbolt controllers
built into Macs which can be put into D3cold with nonstandard ACPI
methods.

Unfortunately we rely on pci_raw_set_power_state()'s current behaviour
in several places: When platform_pci_set_power_state() is called to wake
a device from D3cold, its current_state is not updated even though it is
no longer in D3cold.  Instead, pci_raw_set_power_state() is assumed to
clean up the resulting incongruence.  Fix by setting current_state to
PCI_UNKNOWN after platform_pci_set_power_state().

Also, when a bridge is put into D3cold, its children's current_state is
changed to D3cold in __pci_complete_power_transition().  (Introduced by
commit 448bd857d48e ("PCI/PM: add PCIe runtime D3cold support").) This
doesn't necessarily reflect the children's actual power state: They may
still be powered on, they're just no longer accessible.  However this
shouldn't be a concern because if the children are accessed, their
parent needs to resume anyway and the PM core takes care of this.
Again, pci_raw_set_power_state() is relied upon to clean up the
current_state when the children are resumed the next time.  We cannot
reliably reconstruct the children's current_state when resuming their
parent.  We also shouldn't blindly set it to PCI_UNKNOWN since some
children may actually be turned off and D3cold is their correct
current_state.  Therefore fix by no longer touching the children's
current_state at all.

Cc: Huang Ying <redacted>
Cc: Rafael J. Wysocki <redacted>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
 drivers/pci/pci.c | 43 ++++++++++---------------------------------
 1 file changed, 10 insertions(+), 33 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 95727b4..791dfe7 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c

@@ -612,6 +612,9 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
 	if (!dev->pm_cap)
 		return -EIO;
 
+	if (dev->current_state == PCI_D3cold)
+		return -EIO;
+

 	if (state < PCI_D0 || state > PCI_D3hot)
 		return -EINVAL;
 

@@ -728,8 +731,10 @@ void pci_update_current_state(struct pci_dev *dev, pci_power_t state)
  */
 void pci_power_up(struct pci_dev *dev)
 {
-	if (platform_pci_power_manageable(dev))
+	if (platform_pci_power_manageable(dev)) {
 		platform_pci_set_power_state(dev, PCI_D0);
+		dev->current_state = PCI_UNKNOWN;

+	}
 
 	pci_raw_set_power_state(dev, PCI_D0);
 	pci_update_current_state(dev, PCI_D0);

@@ -746,8 +751,10 @@ static int pci_platform_power_transition(struct pci_dev *dev, pci_power_t state)
 
 	if (platform_pci_power_manageable(dev)) {
 		error = platform_pci_set_power_state(dev, state);
-		if (!error)
+		if (!error) {
+			dev->current_state = PCI_UNKNOWN;

 			pci_update_current_state(dev, state);
+		}
 	} else
 		error = -ENODEV;
 

@@ -809,30 +816,6 @@ static void __pci_start_power_transition(struct pci_dev *dev, pci_power_t state)
 }
 
 /**
- * __pci_dev_set_current_state - Set current state of a PCI device
- * @dev: Device to handle
- * @data: pointer to state to be set
- */
-static int __pci_dev_set_current_state(struct pci_dev *dev, void *data)
-{
-	pci_power_t state = *(pci_power_t *)data;
-
-	dev->current_state = state;
-	return 0;
-}
-
-/**
- * __pci_bus_set_current_state - Walk given bus and set current state of devices
- * @bus: Top bus of the subtree to walk.
- * @state: state to be set
- */
-static void __pci_bus_set_current_state(struct pci_bus *bus, pci_power_t state)
-{
-	if (bus)
-		pci_walk_bus(bus, __pci_dev_set_current_state, &state);
-}
-
-/**
  * __pci_complete_power_transition - Complete power transition of a PCI device
  * @dev: PCI device to handle.
  * @state: State to put the device into.

@@ -841,15 +824,9 @@ static void __pci_bus_set_current_state(struct pci_bus *bus, pci_power_t state)
  */
 int __pci_complete_power_transition(struct pci_dev *dev, pci_power_t state)
 {
-	int ret;
-
 	if (state <= PCI_D0)
 		return -EINVAL;
-	ret = pci_platform_power_transition(dev, state);
-	/* Power off the bridge may power off the whole hierarchy */
-	if (!ret && state == PCI_D3cold)
-		__pci_bus_set_current_state(dev->subordinate, PCI_D3cold);
-	return ret;
+	return pci_platform_power_transition(dev, state);
 }
 EXPORT_SYMBOL_GPL(__pci_complete_power_transition);