Re: [PATCH v11 11/16] iommu/arm-smmu-v3: Add CMDQ_PROD_STOP_FLAG to gate CMDQ submissions

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Oct 01, 2026 at 05:40:41AM +0000, Pranjal Shrivastava wrote:
> On Wed, Sep 30, 2026 at 01:33:58PM -0700, Nicolin Chen wrote:
> > We may get away from the TLB maintenance. But ATC can be the case
> > broken by the stop flag?
> > 
> 
> Not really, I guess Sashiko missed the comment in a later patch. This
> was discussed with Jason in v9 [1].
> 
> The key thing is that ATC_INVs can't be issued by the time we set this
> flag anyway.. if we're in the suspend callback, the PCIe EP is already
> suspended, so none of the ATC invalidation TLPs would be responded to.

Okay.

> I'd addressed this in the RPM patch with a comment right above this check:
> 
>          * Note that eliding ATC invalidations (CMDQ_OP_ATC_INV) is safe
>          * because client PCIe endpoints are guaranteed to be suspended
>          * (via device links) before the SMMU is suspended. With the PCIe
>          * links in a low-power state, no new TLPs can be transmitted.
>          * It is strictly the responsibility of the client/endpoint driver
>          * to quiesce DMA and ensure that the ATC state is cleared across
>          * power state transitions.
> 
> i.e. we only start eliding once *all* consumers are RPM suspended, so
> the "endpoint in D0" scenario can't happen.. and a suspended PCIe
> function shouldn't be issuing translated requests anyway.

Maybe move it to this PATCH-11?

> So we can't issue ATC_INVs during suspend (the EP is already down), nor
> during resume (the SMMU resumes *before* the EP is made active). The EP
> can't use its ATC while suspended, and if it loses power/resets on the
> way back to D0 (from D3cold, or D3hot with No_Soft_Reset=0), it comes 
> back with an empty ATC.. same assumption the PCI reset path makes today
> (pci_dev_reset_iommu_prepare()).

In that case, would the STOP flag be too late? It's only set in
the middle of the SMMU suspend. So, an ATC command (via doamin
invalidation) might be issued prior to the Point of Commitment,
which will be timed out due to the unresponding EP?

Nicolin