[Intel-xe] [PATCH v3] drm/xe/pm: Disable PM on unbounded pcie parent bridge

[Anshuman Gupta <anshuman.gupta@intel.com>]

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 state therefore
assert dev_warn on unbounded VSP and disable xe driver
PM support.

v2:
- Disable Xe PCI PM support. [Rodrigo]
v3:
- Changed subject and Rebase.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
---
 drivers/gpu/drm/xe/xe_pci.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_pci.c b/drivers/gpu/drm/xe/xe_pci.c
index e789a50a1310..e09d76b7755a 100644
--- a/drivers/gpu/drm/xe/xe_pci.c
+++ b/drivers/gpu/drm/xe/xe_pci.c
@@ -603,6 +603,19 @@ static void xe_pci_remove(struct pci_dev *pdev)
 	pci_set_drvdata(pdev, NULL);
 }
 
+static void xe_pci_unbounded_bridge_disable_pm(struct pci_dev *pdev)
+{
+	struct pci_dev *bridge = pci_upstream_bridge(pdev);
+
+	if (!bridge)
+		return;
+
+	if (!bridge->driver) {
+		dev_warn(&pdev->dev, "unbounded parent pci bridge, device won't support any PM support.\n");
+		pdev->driver->driver.pm = NULL;
+	}
+}
+
 static int xe_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
 	const struct xe_device_desc *desc = (const void *)ent->driver_data;
@@ -628,10 +641,13 @@ static int xe_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		return -ENODEV;
 	}
 
+
 	err = xe_display_driver_probe_defer(pdev);
 	if (err)
 		return err;
 
+	xe_pci_unbounded_bridge_disable_pm(pdev);
+
 	xe = xe_device_create(pdev, ent);
 	if (IS_ERR(xe))
 		return PTR_ERR(xe);
-- 
2.38.0