PCI/PM: Set up runtime PM even for devices without PCI PM

JIRA: https://issues.redhat.com/browse/RHEL-90801
Upstream Status: 907a7a2

commit 907a7a2
Author: Mario Limonciello <mario.limonciello@amd.com>
Date:   Wed Jun 11 18:31:16 2025 -0500

    PCI/PM: Set up runtime PM even for devices without PCI PM

    4d4c10f ("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: 4d4c10f ("PCI: Explicitly put devices into D0 when initializing")
    Reported-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
    Closes: https://lore.kernel.org/linux-pci/20250424043232.1848107-1-superm1@kernel.org/T/#m7e8929d6421690dc8bd6dc639d86c2b4db27cbc4
    Reported-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
    Closes: https://lore.kernel.org/linux-pci/20250424043232.1848107-1-superm1@kernel.org/T/#m40d277dcdb9be64a1609a82412d1aa906263e201
    Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Tested-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
    Tested-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
    Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
    Acked-by: Rafael J. Wysocki <rafael@kernel.org>
    Cc: Alex Williamson <alex.williamson@redhat.com>
    Link: https://patch.msgid.link/20250611233117.61810-1-superm1@kernel.org

Signed-off-by: Myron Stowe <mstowe@redhat.com>

Author: Myron Stowe

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);