[PATCH v3] drm/xe/pm: Disable RPM for SR-IOV VFs with no PCIe PM capability

[Satyanarayana K V P]

Enable Runtime Power Management (RPM) for PCI Express devices by utilizing
their native Power Management (PM) capabilities. The specification (as per
section 5.10.1 in PCI Express® Base Specification Revision 7.0) mandates
that Virtual Functions (VFs) without Power Management capability inherit
their associated Physical Function's (PF) power state.

As per PCIe spec "If a VF does not implement the PCI Power Management
Capability, then the VF behaves as if it had been programmed into the
equivalent power state of its associated PF"

Since Intel GPU VFs lack PM capability implementations, VFs power behavior
must mirror their PF's state. During VF creation, the PF remains active
from the PCI subsystem perspective. To maintain consistency, explicitly
disable RPM for VFs missing PM capability to ensure they follow their PF's
power management status rather than entering low-power states
independently.

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>

---
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 | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
index 8aae66660931..019de04fa7bb 100644
--- a/drivers/gpu/drm/xe/xe_pm.c
+++ b/drivers/gpu/drm/xe/xe_pm.c
@@ -246,8 +246,18 @@ 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;
 
+	/*
+	 * Disable RPM for VFs if PM cap is not supported.
+	 * As per PCIe specification, "If a VF does not implement the PCI Power
+	 * Management Capability, then the VF behaves as if it had been programmed
+	 * into the equivalent power state of its associated PF"
+	 */
+	if (!(pdev->pm_cap || !IS_SRIOV_VF(xe)))
+		return;
+
 	/*
 	 * Disable the system suspend direct complete optimization.
 	 * We need to ensure that the regular device suspend/resume functions
@@ -366,8 +376,12 @@ 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;
 
+	if (!(pdev->pm_cap || !IS_SRIOV_VF(xe)))
+		return;
+
 	pm_runtime_get_sync(dev);
 	pm_runtime_forbid(dev);
 }
-- 
2.43.0