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/20241001083438.10070-4-jhp@endlessos.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=218394
Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index 264a180..11870d1 100644 (file)
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -740,11 +740,9 @@ 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
@@ -752,7 +750,7 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
         */
        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;
 }