Re: [PATCH] iommu/arm-smmu: Use pm_runtime in fault handlers

[Akhil P Oommen <akhilpo@oss.qualcomm.com>]

On 1/27/2026 5:41 PM, Prakash Gupta wrote:
> Commit d4a44f0750bb ("iommu/arm-smmu: Invoke pm_runtime across the driver")
> enabled pm_runtime for the arm-smmu device. On systems where the SMMU
> sits in a power domain, all register accesses must be done while the
> device is runtime-resumed to avoid unclocked register reads and
> potential NoC errors.
> 
> So far, this has not been an issue for most SMMU clients because
> stall-on-fault is enabled by default. While a translation fault is
> being handled, the SMMU stalls further translations for that context
> bank, so the fault handler would not race with a powered-down
> SMMU.
> 
> Adreno SMMU now disables stall-on-fault in the presence of fault
> storms to avoid saturating SMMU resources and hanging the GMU. With
> stall-on-fault disabled, the SMMU can generate faults while its power
> domain may no longer be enabled, which makes unclocked accesses to
> fault-status registers in the SMMU fault handlers possible.
> 
> Guard the context and global fault handlers with arm_smmu_rpm_get() /
> arm_smmu_rpm_put() so that all SMMU fault register accesses are done
> with the SMMU powered.
> 
> Fixes: b13044092c1e ("drm/msm: Temporarily disable stall-on-fault after a page fault")
> Co-developed-by: Pratyush Brahma <pratyush.brahma@oss.qualcomm.com>
> Signed-off-by: Pratyush Brahma <pratyush.brahma@oss.qualcomm.com>
> Signed-off-by: Prakash Gupta <prakash.gupta@oss.qualcomm.com>

Acked-by: Akhil P Oommen <akhilpo@oss.qualcomm.com>

-Akhil