PCI: vmd: Set devices to D0 before enabling PM L1 Substates

JIRA: https://issues.redhat.com/browse/RHEL-47438
Upstream Status: d660410

commit d660410
Author: Jian-Hong Pan <[email protected]>
Date:   Tue Oct 1 16:34:38 2024 +0800

    PCI: vmd: Set devices to D0 before enabling PM L1 Substates

    The remapped PCIe Root Port and the child device have PM L1 Substates
    capability, but they are disabled originally.

    Here is a failed example on ASUS B1400CEAE:

      Capabilities: [900 v1] L1 PM Substates
            L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1- L1_PM_Substates+
                      PortCommonModeRestoreTime=32us PortTPowerOnTime=10us
            L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
                       T_CommonMode=0us LTR1.2_Threshold=101376ns
            L1SubCtl2: T_PwrOn=50us

    Enable PCI-PM L1 PM Substates for devices below VMD while they are in D0
    (see PCIe r6.0, sec 5.5.4).

    Link: https://lore.kernel.org/r/[email protected]
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=218394
    Signed-off-by: Jian-Hong Pan <[email protected]>
    Signed-off-by: Krzysztof Wilczyński <[email protected]>
    Signed-off-by: Bjorn Helgaas <[email protected]>
    Reviewed-by: Kuppuswamy Sathyanarayanan <[email protected]>

Signed-off-by: Myron Stowe <[email protected]>

Author: Myron Stowe

drivers/pci/controller/vmd.c

@@ -740,19 +740,17 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
 	if (!(features & VMD_FEAT_BIOS_PM_QUIRK))
 		return 0;
 
-	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
-
 	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
 	if (!pos)
-		return 0;
+		goto out_state_change;
 
 	/*
 	 * Skip if the max snoop LTR is non-zero, indicating BIOS has set it
 	 * so the LTR quirk is not needed.
 	 */
 	pci_read_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, &ltr_reg);
 	if (!!(ltr_reg & (PCI_LTR_VALUE_MASK | PCI_LTR_SCALE_MASK)))
-		return 0;
+		goto out_state_change;
 
 	/*
 	 * Set the default values to the maximum required by the platform to
@@ -764,6 +762,13 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
 	pci_write_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, ltr_reg);
 	pci_info(pdev, "VMD: Default LTR value set by driver\n");
 
+out_state_change:
+	/*
+	 * Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
+	 * PCIe r6.0, sec 5.5.4.
+	 */
+	pci_set_power_state_locked(pdev, PCI_D0);
+	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
 	return 0;
 }