[PATCH v4] PCI/PM: Target PM state is D3hot if device can only generate PME from D3cold

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Some PCIe devices only support PME (Power Management Event) from D3cold.
One example is ASMedia xHCI controller:

11:00.0 USB controller: ASMedia Technology Inc. ASM1042A USB 3.0 Host Controller (prog-if 30 [XHCI])
  ...
  Capabilities: [78] Power Management version 3
  	  Flags: PMEClk- DSI- D1- D2- AuxCurrent=55mA PME(D0-,D1-,D2-,D3hot-,D3cold+)
	  Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-

With such devices, if it has wake enabled, the kernel selects lowest
possible power state to be D0 in pci_target_state(). This is problematic
because it prevents the root port it is connected to enter low power
state too which makes the system consume more energy than necessary.

The problem in pci_target_state() is that it only accounts the "current"
device state, so when the bridge above it (a root port for instance) is
transitioned into D3hot the device transitions into D3cold. This is
because when the root port is first transitioned into D3hot then the
ACPI power resource is turned off which puts the PCIe link to L2/L3 (and
the root port and the device are in D3cold). If the root port is kept in
D3hot it still means that the device below it is still effectively in
D3cold as no configuration messages pass through. Furthermore the
implementation note of PCIe 5.0 sec 5.3.1.4 says that the device should
expect to be transitioned into D3cold soon after its link transitions
into L2/L3 Ready state.

Taking the above into consideration, instead of forcing the device stay
in D0 we modify pci_target_state() to return D3hot in this special case
and make __pci_enable_wake() to enable PME too in this case.

Reported-by: Utkarsh H Patel <utkarsh.h.patel@intel.com>
Reported-by: Koba Ko <koba.ko@canonical.com>
Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
The previous version of the patch is here:

https://lore.kernel.org/linux-pm/20210616150516.28242-1-mika.westerberg@linux.intel.com/

Changes from the previous version:

  * Dropped redundant test in pci_target_state().

 drivers/pci/pci.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b717680377a9..043c5c304308 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2485,7 +2485,13 @@ static int __pci_enable_wake(struct pci_dev *dev, pci_power_t state, bool enable
 	if (enable) {
 		int error;
 
-		if (pci_pme_capable(dev, state))
+		/*
+		 * Enable PME if device is capable from given state.
+		 * Special case is device that can only generate PME
+		 * from D3cold then we enable PME too.
+		 */
+		if (pci_pme_capable(dev, state) ||
+		    (state == PCI_D3hot && pci_pme_capable(dev, PCI_D3cold)))
 			pci_pme_active(dev, true);
 		else
 			ret = 1;
@@ -2595,6 +2601,14 @@ static pci_power_t pci_target_state(struct pci_dev *dev, bool wakeup)
 		 * PME#.
 		 */
 		if (dev->pme_support) {
+			/*
+			 * Special case if device supports only PME from
+			 * D3cold but not from D3hot we still return D3hot.
+			 */
+			if (target_state == PCI_D3hot &&
+				(dev->pme_support & (1 << PCI_D3cold)))
+				return target_state;
+
 			while (target_state
 			      && !(dev->pme_support & (1 << target_state)))
 				target_state--;
-- 
2.30.2