[PATCH] PCI/PM: Don't call pci_pm_power_up_and_verify_state() for devices already in D0

[Rich Hanes <georgebastille@gmail.com>]

Commit 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when
initializing") calls pci_pm_power_up_and_verify_state() for every PCI
device at the end of pci_pm_init().  This causes a boot-time regression
on PCIe endpoints that the firmware leaves in D0.

The problem is not the _PS0 call itself — pci_power_up() returns early
when the hardware PM_CTRL register already reads D0.  The problem is
that pci_pm_power_up_and_verify_state() unconditionally calls
pci_update_current_state() afterwards, which sets current_state to
PCI_D0 even for devices that were never actually transitioned.

pcie_aspm_init_link_state() later checks current_state when the
pcieport driver binds to the upstream port.  From aspm.c:

  /* Spec says both ports must be in D0 before enabling PCI PM substates */
  if (parent->current_state != PCI_D0 || child->current_state != PCI_D0) {
          state &= ~PCIE_LINK_STATE_L1_SS_PCIPM;

When current_state is PCI_D0 (set prematurely by pci_pm_init()), ASPM
enables L1 PM substates including L1.2.  L1.2 removes the PCIe
reference clock from the link during idle periods, putting the
downstream device into a D3cold-equivalent state.  Without a subsequent
_PS0 call to restore it, the device does not respond to config space
reads when the link returns to L0.  pciehp observes this as:

  pciehp: Slot(0): Card not present   <- L1.2 entry during link retrain
  pciehp: Slot(0): Card present
  pciehp: Slot(0): Link Up
  pciehp: Slot(0): No device found    <- device unresponsive in D3cold

Reproduced on a Lenovo ThinkPad with Intel Wireless-AC 7265 (8086:095a)
behind PCIe root port 8086:9d10.  The workaround pcie_aspm=off confirms
that suppressing L1 PM substate configuration prevents the failure.

The fix is to read PM_CTRL before calling 
pci_pm_power_up_and_verify_state() and skip it when the hardware already 
reports D0.  This preserves the
_REG notification for devices the firmware leaves in a non-D0 state
(the original motivation for the commit) while leaving current_state as
PCI_UNKNOWN for devices already in D0, which correctly defers L1 PM
substate enablement.

Also add an early return to pci_power_up() to avoid calling
platform_pci_set_power_state() (_PS0) redundantly on devices whose
hardware state is already D0 and whose software state is PCI_UNKNOWN.

Fixes: 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when initializing")
Cc: stable@vger.kernel.org
Cc: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Rich Hanes <georgebastille@gmail.com>
---
 drivers/pci/pci.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8479c2e1f74f..e2e11b2884d4 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1301,6 +1301,13 @@ int pci_power_up(struct pci_dev *dev)
 	pci_power_t state;
 	u16 pmcsr;
 
+	if (dev->pm_cap && dev->current_state == PCI_UNKNOWN && !pci_dev_is_disconnected(dev)) {
+		pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
+		if (!PCI_POSSIBLE_ERROR(pmcsr) && (pmcsr & PCI_PM_CTRL_STATE_MASK) == PCI_D0) {
+			dev->current_state = PCI_D0;
+			return 0;
+		}
+	}
 	platform_pci_set_power_state(dev, PCI_D0);
 
 	if (!dev->pm_cap) {
@@ -3191,7 +3198,27 @@ void pci_pm_init(struct pci_dev *dev)
 	}
 
 poweron:
-	pci_pm_power_up_and_verify_state(dev);
+	/*
+	 * Explicitly put the device into D0 to ensure platform power methods
+	 * such as _PS0 are called and _REG is notified.  Only do this when
+	 * the hardware is not already in D0: pcie_aspm_init_link_state()
+	 * enables PCIe L1 PM substates (L1.1/L1.2) only when both the
+	 * downstream device and its parent report current_state == PCI_D0.
+	 * Calling pci_pm_power_up_and_verify_state() for a device already in
+	 * D0 would set current_state prematurely, enabling L1.2 before the
+	 * driver is ready and causing the device to enter a deep sleep state
+	 * it cannot exit without platform intervention (_PS0).
+	 */
+	if (dev->pm_cap) {
+		u16 pmcsr;
+
+		pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
+		if (PCI_POSSIBLE_ERROR(pmcsr) ||
+		    (pmcsr & PCI_PM_CTRL_STATE_MASK) != PCI_D0)
+			pci_pm_power_up_and_verify_state(dev);
+	} else {
+		pci_pm_power_up_and_verify_state(dev);
+	}
 	pm_runtime_forbid(&dev->dev);
 
 	/*
-- 
2.53.0