Re: [PATCH v2] memory: mtk-smi: fail larb runtime resume until component bind

[Krzysztof Kozlowski <krzk@kernel.org>]

On 26/09/2026 21:24, Valentin Haudiquet wrote:
> 
> Publish the bind state with smp_store_release() and check it with
> smp_load_acquire() in mtk_smi_larb_resume(); that answers how the
> check synchronizes between CPUs.  Fail the resume with -EAGAIN: the
> larb stays RPM_SUSPENDED and retryable, the error is dropped by
> pm_runtime_get_suppliers() on the driver-core probe path, and the
> consumer's first runtime resume after the bind (at display enable,
> mtk_crtc_atomic_enable()) re-runs the callback, which configures the

Do not describe obvious patch contents. You wrote huge wall of text,
instead of keeping it concise and informative.


> larb ports then.  Failing rather than skipping keeps the larb
> suspended instead of marking it active with unconfigured MMU ports,
> which would only turn the crash into silent iommu faults.
> 
> A failed supplier resume does not break the consumer's probe.
> pm_runtime_get_suppliers() is void and drops the error, so a probe
> inside the window just proceeds.  The display components do not touch
> the larb in probe: mtk_disp_ovl_probe() and its siblings only call
> pm_runtime_enable(), and mdp3 only enables runtime PM for its
> DMA-capable components (mtk-mdp3-comp.c).  The first real runtime
> resume happens later, at display enable: mtk_crtc_atomic_enable()
> does pm_runtime_resume_and_get() and the device links resume the
> larb first.  By then the component master bind has completed, so the
> larb configures its ports and the resume succeeds.  There is no
> deadlock either: the bind only records the larb pointers, it does not
> resume the larb, so the window closes when the bind completes
> regardless of what consumers do.  -ENODEV is not an alternative;
> like -EPROBE_DEFER it is recorded in dev->power.runtime_error
> instead of being exempted.
> 
> The bind state is a separate flag rather than a NULL test on
> larb->mmu so that the publication explicitly covers both larb->mmu
> and larb->bank.  mtk_smi_larb_unbind() clears it again with
> WRITE_ONCE(), which is all the clear side needs since it publishes
> nothing, so an iommu removal or module unload can not leave a stale
> bound state pointing at the freed iommu data.  A resume in flight
> while the iommu goes away is a pre-existing teardown hazard (the
> data it reads belongs to the iommu device, whose removal breaks
> bound consumers anyway); clearing the flag makes every resume that
> starts after the clear fail safely instead.

All this looks LLM generated. Don't send LLM explanation to people. It's
only for you.

> 
> Tested on MT8183 (krane) with the full MTK stack built as modules:
> with this change applied the machine boots reliably, the iommu
> probes and binds all larbs, and the display stack comes up fully
> functional.
> 
> The Fixes: tag points at 4f0a1a1ae351, which moved the port
> configuration into the runtime resume.  The device links that open
> the race window are added on the mtk-iommu side, but the dereference
> guarded here is the one that commit introduced.


I do not see how is this relevant.

Best regards,
Krzysztof