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

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Fri, Aug 01, 2025 at 10:00:17PM +0530, Satyanarayana K V P wrote:
> 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

If this is a true statement your patch below is wrong.
It should simply be if (IS_VF) return;

> 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@intel.com>
> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Michał Winiarski <michal.winiarski@intel.com>
> Cc: Anshuman Gupta <anshuman.gupta@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@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
>