linux-kernel - [RFC 2/2] PCI: vmd: Provide default ASPM link state for synthetic hierarchy

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Message-ID: <20250717004034.2998443-3-david.e.box@linux.intel.com>
Date: Wed, 16 Jul 2025 17:40:26 -0700
From: "David E. Box" <david.e.box@...ux.intel.com>
To: rafael@...nel.org,
	bhelgaas@...gle.com,
	vicamo.yang@...onical.com,
	kenny@...ix.com,
	nirmal.patel@...ux.intel.com
Cc: "David E. Box" <david.e.box@...ux.intel.com>,
	linux-pm@...r.kernel.org,
	linux-pci@...r.kernel.org,
	ilpo.jarvinen@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: [RFC 2/2] PCI: vmd: Provide default ASPM link state for synthetic hierarchy

Devices behind the VMD controller reside on a synthetic PCIe hierarchy that
is not visible to ACPI and not configured by firmware. As a result, these
devices receive no ASPM defaults from the BIOS, and ASPM remains disabled
unless explicitly enabled later.

Now that the ASPM core supports driver-supplied default link states via
pci_bus->aspm_bus_link_state, set this field on the VMD root bus to enable
ASPM for devices in the VMD domain. This ensures the platform's intended
power-saving configuration is applied during initialization without
requiring any special-case logic in the ASPM core.

Link: https://lore.kernel.org/linux-pm/0b166ece-eeec-ba5d-2212-50d995611cef@panix.com
Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
---
 drivers/pci/controller/vmd.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index 8df064b62a2f..a0d4e96ce872 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -730,7 +730,7 @@ static void vmd_copy_host_bridge_flags(struct pci_host_bridge *root_bridge,
 }
 
 /*
- * Enable ASPM and LTR settings on devices that aren't configured by BIOS.
+ * Enable LTR settings on devices that aren't configured by BIOS.
  */
 static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
 {
@@ -770,7 +770,6 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
 	 * 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;
 }
 
@@ -911,6 +910,10 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
 		return -ENODEV;
 	}
 
+#ifdef CONFIG_PCIEASPM
+	vmd->bus->aspm_bus_link_state = PCIE_LINK_STATE_ALL;
+#endif
+
 	vmd_copy_host_bridge_flags(pci_find_host_bridge(vmd->dev->bus),
 				   to_pci_host_bridge(vmd->bus->bridge));
 
-- 
2.43.0