Re: [PATCH v3] iommu/arm-smmu: Use pm_runtime in fault handlers

[Pranjal Shrivastava <praan@google.com>]

On Tue, Jun 30, 2026 at 02:32:46PM +0530, Prakash Gupta wrote:

Hi Prakash,

> 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 active 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_if_active() and arm_smmu_rpm_put() so that all SMMU
> fault register accesses are done with the SMMU powered. If the SMMU is
> not runtime active, the fault can be safely ignored as
> arm_smmu_device_reset() clears fault registers on resume.
> 
> Additionally, disable fault reporting in arm_smmu_runtime_suspend()
> before powering down. pm_runtime_get_if_active() returns 0 during
> RPM_SUSPENDING, so without this, level-triggered fault interrupts would
> cause an interrupt storm while the device is being suspended.
> arm_smmu_device_reset() re-enables fault reporting on resume.
> 
> 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>
> ---
> Changes in v3:
> - Add arm_smmu_rpm_get_if_active() wrapper that returns 1 when pm_runtime
>   is disabled, ensuring fault handlers work on non-pm_runtime systems
> - Disable fault reporting in arm_smmu_runtime_suspend() before powering
>   down to prevent interrupt storms during RPM_SUSPENDING state
> - Use pm_runtime_put_autosuspend() in arm_smmu_rpm_put() instead of
>   private __pm_runtime_put_autosuspend()
> - Link to v2: https://patch.msgid.link/20260313-smmu-rpm-v2-1-8c2236b402b0@oss.qualcomm.com
> 
> Changes in v2:
> - Switched from arm_smmu_rpm_get()/arm_smmu_rpm_put() wrappers to
>   pm_runtime_get_if_active()/pm_runtime_put_autosuspend() APIs
> - Added support for smmu->impl->global_fault callback in global fault handler
> - Remove threaded irq context fault restriction to allow modifying stall
>   mode for adreno smmu
> - Link to v1: https://patch.msgid.link/20260127-smmu-rpm-v1-1-2ef2f4c85305@oss.qualcomm.com
> ---
>  drivers/iommu/arm/arm-smmu/arm-smmu.c | 92 +++++++++++++++++++++++++----------
>  1 file changed, 67 insertions(+), 25 deletions(-)
> 

[...]

This version looks fine to me, 
Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan