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

[Matthew Brost]

On Mon, Aug 18, 2025 at 11:13:32AM +0100, Matthew Auld wrote:
> On 18/08/2025 03:13, Matthew Brost wrote:
> > On Sun, Aug 17, 2025 at 12:40:55PM -0400, Rodrigo Vivi wrote:
> > > On Tue, Aug 12, 2025 at 10:06:13PM +0530, Satyanarayana K V P wrote:
> > > > 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>
> > > 
> > > Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > > 
> > > and pushing
> > > 
> > 
> > This might need a little more thought(?). What are the full consequences
> > of this patch? For example, will xe_pm_suspend()/xe_pm_resume() never be
> > called on a VF? I think that’s correct and desirable, but consider code
> > paths like:
> > 
> > if (xe_pm_runtime_get_if_active())
> >          /* Take action assuming GPU state is valid */
> > else
> >          /* Take action assuming GPU state has been lost */
> > 
> > 
> > On a VF, this is now broken, since we don’t lose GPU state—unless I’m
> > missing something, or xe_pm_runtime_get_if_active() always returns true
> > on a VF which in that case we should be good.
> 
> It should behave as though the system is always RPM_ACTIVE with an elevated
> refcount (since driver is no longer dropping the refcount to turn on RPM)
> which will make it always return true for if_active() and others.
> 

Thanks for the explaination. I see patches out there to remove the GuC
reload from Dc3 hot path too, so maybe the case I raised isn't even
valid.

Matt 

> > 
> > Matt
> > 
> > > > 
> > > > ---
> > > > 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
> > > > 
>