[PATCH] drm/amdgpu: check ASPM on the dGPU host link

dGPUs with an internal PCIe switch expose graphics functions below the
switch downstream port. The automatic ASPM check uses the display
endpoint and evaluates the internal link instead of the host link.

Use the switch upstream port for the check and report the selected
link.

Fixes: 0ab5d711ec74 ("drm/amd: Refactor `amdgpu_aspm` to be evaluated per device")
Signed-off-by: Yang Wang <[email protected]>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 50 +++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 2b9799033174..e68a5ddcae69 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -1344,6 +1344,31 @@ static bool amdgpu_device_aspm_support_quirk(struct amdgpu_device *adev)
 #endif
 }
 
+/*
+ * Some dGPUs expose their display endpoint below an internal PCIe switch.
+ * Use the switch upstream port to query the host-facing link.
+ */
+static struct pci_dev *amdgpu_device_get_aspm_pdev(struct amdgpu_device *adev)
+{
+	struct pci_dev *swds, *swus;
+
+	swds = pci_upstream_bridge(adev->pdev);
+	if (!swds ||
+	    (swds->vendor != PCI_VENDOR_ID_ATI &&
+	     swds->vendor != PCI_VENDOR_ID_AMD) ||
+	    pci_pcie_type(swds) != PCI_EXP_TYPE_DOWNSTREAM)
+		return adev->pdev;
+
+	swus = pci_upstream_bridge(swds);
+	if (!swus ||
+	    (swus->vendor != PCI_VENDOR_ID_ATI &&
+	     swus->vendor != PCI_VENDOR_ID_AMD) ||
+	    pci_pcie_type(swus) != PCI_EXP_TYPE_UPSTREAM)
+		return adev->pdev;
+
+	return swus;
+}
+
 /**
  * amdgpu_device_should_use_aspm - check if the device should program ASPM
  *
@@ -1356,6 +1381,9 @@ static bool amdgpu_device_aspm_support_quirk(struct amdgpu_device *adev)
  */
 bool amdgpu_device_should_use_aspm(struct amdgpu_device *adev)
 {
+	struct pci_dev *aspm_pdev, *parent;
+	bool enabled;
+
 	switch (amdgpu_aspm) {
 	case -1:
 		break;
@@ -1370,7 +1398,27 @@ bool amdgpu_device_should_use_aspm(struct amdgpu_device *adev)
 		return false;
 	if (amdgpu_device_aspm_support_quirk(adev))
 		return false;
-	return pcie_aspm_enabled(adev->pdev);
+
+	/*
+	 * pcie_aspm_enabled() checks the link between its argument and
+	 * the immediate upstream bridge. Use SWUS for dGPUs with an
+	 * internal switch so that this is the host-facing link.
+	 */
+	aspm_pdev = amdgpu_device_get_aspm_pdev(adev);
+	parent = pci_upstream_bridge(aspm_pdev);
+	if (!parent) {
+		dev_info(adev->dev, "ASPM: no upstream PCIe link for %s\n",
+			 pci_name(aspm_pdev));
+		return false;
+	}
+
+	enabled = pcie_aspm_enabled(aspm_pdev);
+	/* Report the exact link used for the automatic ASPM decision. */
+	dev_info(adev->dev, "ASPM: link %s <-> %s is %s\n",
+		 pci_name(parent), pci_name(aspm_pdev),
+		 enabled ? "enabled" : "disabled");
+
+	return enabled;
 }
 
 /* if we get transitioned to only one device, take VGA back */
-- 
2.54.0