Re: My AlderLake Dell (XPS-9320) needs these patches to get full standby/low-power modes

[Kenneth Crudup <kenny@panix.com>]

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Or, just use (some version of) the attached patch (against Linus' recent 
master) that enables VMD ASPM this for us "automatically" if there's a 
detected VMD ?

I'd prefer a scalpel to a bludgeon (and have been trying to get some 
version of these fixes into mainline for a while).

-Kenny

On 12/19/24 11:52, David E. Box wrote:

> If you want to override this behavior, you can try setting pcie_aspm=force on
> the kernel command line.

-- 
Kenneth R. Crudup / Sr. SW Engineer, Scott County Consulting, Orange 
County CA

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diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 28567d457613..a5df6230cf3c 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -768,6 +768,31 @@ static void aspm_l1ss_init(struct pcie_link_state *link)
 		aspm_calc_l12_info(link, parent_l1ss_cap, child_l1ss_cap);
 }
 
+/*
+ * BIOS may not be able to access config space of devices under VMD domain, so
+ * it relies on software to enable ASPM for links under VMD.
+ */
+static bool pci_fixup_vmd_bridge_enable_aspm(struct pci_dev *pdev)
+{
+       struct pci_bus *bus = pdev->bus;
+       struct device *dev;
+       struct pci_driver *pdrv;
+
+       if (!pci_is_root_bus(bus))
+               return false;
+
+       dev = bus->bridge->parent;
+       if (dev == NULL)
+               return false;
+
+       pdrv = pci_dev_driver(to_pci_dev(dev));
+       if (pdrv == NULL || strcmp("vmd", pdrv->name))
+               return false;
+
+       pci_info(pdev, "enable ASPM for pci bridge behind vmd");
+       return true;
+}
+
 static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 {
 	struct pci_dev *child = link->downstream, *parent = link->pdev;
@@ -846,7 +871,8 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 	}
 
 	/* Save default state */
-	link->aspm_default = link->aspm_enabled;
+	link->aspm_default = pci_fixup_vmd_bridge_enable_aspm(parent) ?
+		PCIE_LINK_STATE_ASPM_ALL : link->aspm_enabled;
 
 	/* Setup initial capable state. Will be updated later */
 	link->aspm_capable = link->aspm_support;