[PATCH v6] drm/xe/pm: Disable RPM for SR-IOV VFs

[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 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>

---
V5 -> V6:
- Updated comment (Rodrigo).

V4 -> V5:
- Disable RPM for VFs without checking pm_cap (Rodrigo).
- Updated commit title.

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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
index 5e8126ca8e27..51934d5dc44f 100644
--- a/drivers/gpu/drm/xe/xe_pm.c
+++ b/drivers/gpu/drm/xe/xe_pm.c
@@ -247,6 +247,10 @@ static void xe_pm_runtime_init(struct xe_device *xe)
 {
 	struct device *dev = xe->drm.dev;
 
+	/* Our current VFs do not support RPM. so, disable it */
+	if (IS_SRIOV_VF(xe))
+		return;
+
 	/*
 	 * Disable the system suspend direct complete optimization.
 	 * We need to ensure that the regular device suspend/resume functions
@@ -367,6 +371,10 @@ static void xe_pm_runtime_fini(struct xe_device *xe)
 {
 	struct device *dev = xe->drm.dev;
 
+	/* Our current VFs do not support RPM. so, disable it */
+	if (IS_SRIOV_VF(xe))
+		return;
+
 	pm_runtime_get_sync(dev);
 	pm_runtime_forbid(dev);
 }
-- 
2.43.0