drm/xe/pm: Disable PM on unbounded pcie parent bridge

Intel Discrete GFX cards gfx may have multiple PCIe endpoints,
they connects to root port via pcie upstream switch port(USP)
and virtual pcie switch port(VSP), sometimes VSP pcie devices
doesn't bind to pcieport driver. Without pcieport driver, pcie PM
comes without any warranty and with unbounded VSP gfx card won't
transition to low power pcie Device and Link states therefore
assert drm_warn on unbounded VSP and disable xe driver
PM support.

v2:
- Disable Xe PCI PM support. [Rodrigo]
v3:
- Changed subject and Rebase.
v4:
- %s/xe_pci_unbounded_bridge_disable_pm/xe_assert_on_unbounded_bridge.
  [Rodrigo]
- Use device_set_pm_not_required() instead of dev_pm_ops NULL assignment.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230524090653.1192566-1-anshuman.gupta@intel.comSigned-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_pci.c

@@ -617,6 +617,7 @@ static int xe_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (IS_ERR(xe))
 		return PTR_ERR(xe);
 
+	xe_pm_assert_unbounded_bridge(xe);
 	subplatform_desc = find_subplatform(xe, desc);
 
 	err = xe_info_init(xe, desc, subplatform_desc);

drivers/gpu/drm/xe/xe_pm.c

@@ -214,3 +214,17 @@ int xe_pm_runtime_get_if_active(struct xe_device *xe)
 	WARN_ON(pm_runtime_suspended(xe->drm.dev));
 	return pm_runtime_get_if_active(xe->drm.dev, true);
 }
+
+void xe_pm_assert_unbounded_bridge(struct xe_device *xe)
+{
+	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
+	struct pci_dev *bridge = pci_upstream_bridge(pdev);
+
+	if (!bridge)
+		return;
+
+	if (!bridge->driver) {
+		drm_warn(&xe->drm, "unbounded parent pci bridge, device won't support any PM support.\n");
+		device_set_pm_not_required(&pdev->dev);
+	}
+}

drivers/gpu/drm/xe/xe_pm.h

@@ -21,5 +21,6 @@ int xe_pm_runtime_get(struct xe_device *xe);
 int xe_pm_runtime_put(struct xe_device *xe);
 bool xe_pm_runtime_resume_if_suspended(struct xe_device *xe);
 int xe_pm_runtime_get_if_active(struct xe_device *xe);
+void xe_pm_assert_unbounded_bridge(struct xe_device *xe);
 
 #endif