[SRU P/N][PATCH 1/1] PCI/PM: Set up runtime PM even for devices without PCI PM

[Stefan Bader]

From: Mario Limonciello <mario.limonciello at amd.com>

BugLink: https://bugs.launchpad.net/bugs/2117494

4d4c10f763d7 ("PCI: Explicitly put devices into D0 when initializing")
intended to put PCI devices into D0, but in doing so unintentionally
changed runtime PM initialization not to occur on devices that don't
support PCI PM.  This caused a regression in vfio-pci due to an imbalance
with its use.

Adjust the logic in pci_pm_init() so that even if PCI PM isn't supported
runtime PM is still initialized.

Fixes: 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when initializing")
Reported-by: Giovanni Cabiddu <giovanni.cabiddu at intel.com>
Closes: https://lore.kernel.org/linux-pci/20250424043232.1848107-1-superm1@kernel.org/T/#m7e8929d6421690dc8bd6dc639d86c2b4db27cbc4
Reported-by: Nicolas Dichtel <nicolas.dichtel at 6wind.com>
Closes: https://lore.kernel.org/linux-pci/20250424043232.1848107-1-superm1@kernel.org/T/#m40d277dcdb9be64a1609a82412d1aa906263e201
Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
Tested-by: Giovanni Cabiddu <giovanni.cabiddu at intel.com>
Tested-by: Nicolas Dichtel <nicolas.dichtel at 6wind.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy at linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael at kernel.org>
Cc: Alex Williamson <alex.williamson at redhat.com>
Link: https://patch.msgid.link/20250611233117.61810-1-superm1@kernel.org
Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
---
 drivers/pci/pci.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e9448d55113b..9e42090fb108 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3217,14 +3217,14 @@ void pci_pm_init(struct pci_dev *dev)
 	/* find PCI PM capability in list */
 	pm = pci_find_capability(dev, PCI_CAP_ID_PM);
 	if (!pm)
-		return;
+		goto poweron;
 	/* Check device's ability to generate PME# */
 	pci_read_config_word(dev, pm + PCI_PM_PMC, &pmc);
 
 	if ((pmc & PCI_PM_CAP_VER_MASK) > 3) {
 		pci_err(dev, "unsupported PM cap regs version (%u)\n",
 			pmc & PCI_PM_CAP_VER_MASK);
-		return;
+		goto poweron;
 	}
 
 	dev->pm_cap = pm;
@@ -3269,6 +3269,7 @@ void pci_pm_init(struct pci_dev *dev)
 	pci_read_config_word(dev, PCI_STATUS, &status);
 	if (status & PCI_STATUS_IMM_READY)
 		dev->imm_ready = 1;
+poweron:
 	pci_pm_power_up_and_verify_state(dev);
 	pm_runtime_forbid(&dev->dev);
 	pm_runtime_set_active(&dev->dev);
-- 
2.43.0