[PATCH v4] drm/xe/pm: Disable RPM for SR-IOV VFs with no PCIe PM capability

[Satyanarayana K V P]

VFs without native PCIe Power Management (PM) capabilities inherit their
PF's power state as per PCIe specifications(§5.10.1 PCIe Base Spec 7.0).
Enabling Runtime Power Management (RPM) for these VFs trigger unnecessary
driver suspend/resume operations that ultimately perform no PCI-level power
transition.

Since VFs without PM capabilities cannot independently enter low-power
states, the existing RPM workflow becomes redundant:
1. Driver executes full suspend/resume sequence
2. PCI PM transition step becomes no-op
3. VF power state remains tied to PF's status

Disabling RPM for PM-incapable VFs eliminates this redundant processing
while maintaining proper power management through PF dependency. This
optimization ensures VFs follow their PF's power state without superfluous
runtime handling.

Signed-off-by: Satyanarayana K V P <satyanarayana.k.v.p at intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
Cc: Matthew Brost <matthew.brost at intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
Cc: Anshuman Gupta <anshuman.gupta at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Maarten Lankhorst <dev at lankhorst.se>
---
V3 -> V4:
- Fixed review comments (Rodrigo & Maarten)

V2 -> V3:
- Fixed review comments (Michal Wajdeczko).

V1 -> V2:
- Disable RPM only for VF devices when PM cap is not implemented.
---
 drivers/gpu/drm/xe/xe_pm.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
index 5e8126ca8e27..9d62d3f99ed9 100644
--- a/drivers/gpu/drm/xe/xe_pm.c
+++ b/drivers/gpu/drm/xe/xe_pm.c
@@ -245,8 +245,13 @@ static bool xe_pm_pci_d3cold_capable(struct xe_device *xe)
 
 static void xe_pm_runtime_init(struct xe_device *xe)
 {
+	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
 	struct device *dev = xe->drm.dev;
 
+	/* For VF that doesn't implement pm_caps, the rpm functions are no-op */
+	if (IS_SRIOV_VF(xe) && !pdev->pm_cap)
+		return;
+
 	/*
 	 * Disable the system suspend direct complete optimization.
 	 * We need to ensure that the regular device suspend/resume functions
@@ -365,8 +370,13 @@ int xe_pm_init(struct xe_device *xe)
 
 static void xe_pm_runtime_fini(struct xe_device *xe)
 {
+	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
 	struct device *dev = xe->drm.dev;
 
+	/* For VF that doesn't implement pm_caps, the rpm functions are no-op */
+	if (IS_SRIOV_VF(xe) && !pdev->pm_cap)
+		return;
+
 	pm_runtime_get_sync(dev);
 	pm_runtime_forbid(dev);
 }
-- 
2.43.0