Re: [PATCH v2] iommu: arm-smmu-qcom: Ensure smmu is powered up in set_ttbr0_cfg

[Anna Maniscalco <anna.maniscalco2000@gmail.com>]

On 5/7/26 4:47 PM, Robin Murphy wrote:
> On 25/03/2026 9:11 pm, Anna Maniscalco wrote:
>> Previously the device was being accessed while potentially in a
>> suspended state.
>
> The SMMU driver's own write_context_bank() calls all look to be safely 
> within arm_smmu_rpm_get() scopes that are holding an RPM count when 
> relevant (or the one at probe time before RPM is activated at all), so 
> indeed this seems like the appropriate solution for here where we're 
> free to assume that Adreno platforms must always have a power domain.
>
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
>
> Just a minor nit: it's probably OK in this case (unless Will 
> disagrees), but for future patches, it's preferable for the commit 
> message to be self-contained, so as to give a sufficiently clear 
> description of the problem, and summary of the solution, without 
> having to be read in the context of the title and the whole diff to 
> make sense. For example, if I were writing this I'd put it something 
> like:
>
> "
>   iommu/arm-smmu-qcom: Ensure SMMU is powered up in set_ttbr0_cfg
>
>   arm_smmu_write_context_bank() assumes it is being called with RPM
>   active, but it turns out that is not guaranteed in the path from
>   qcom_adreno_smmu_set_ttbr0_cfg(), so it's possible for the the
>   register accesses to lead to an [external abort/hang/whatever] when
>   [doing whatever it is] while the GPU is idle. Add the RPM calls here
>   to make sure the SMMU is active before we touch it.
> "
>
> Thanks,
> Robin.
Thanks for the feedback, I've sent a v3 with an improved commit message.
>
>> Signed-off-by: Anna Maniscalco <anna.maniscalco2000@gmail.com>
>> ---
>> Changes in v2:
>> - Simplify patch by acquiring device just around the call that needs it
>> - Link to v1: 
>> https://lore.kernel.org/r/20260210-qcom_smmu_pmfix-v1-1-78b7143ac053@gmail.com
>> ---
>>   drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c 
>> b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>> index 573085349df3..cab7d110aaf5 100644
>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>> @@ -231,6 +231,7 @@ static int qcom_adreno_smmu_set_ttbr0_cfg(const 
>> void *cookie,
>>       struct io_pgtable *pgtable = 
>> io_pgtable_ops_to_pgtable(smmu_domain->pgtbl_ops);
>>       struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
>>       struct arm_smmu_cb *cb = &smmu_domain->smmu->cbs[cfg->cbndx];
>> +    int ret;
>>         /* The domain must have split pagetables already enabled */
>>       if (cb->tcr[0] & ARM_SMMU_TCR_EPD1)
>> @@ -260,8 +261,16 @@ static int qcom_adreno_smmu_set_ttbr0_cfg(const 
>> void *cookie,
>>           cb->ttbr[0] |= FIELD_PREP(ARM_SMMU_TTBRn_ASID, cb->cfg->asid);
>>       }
>>   +    ret = pm_runtime_resume_and_get(smmu_domain->smmu->dev);
>> +    if (ret < 0) {
>> +        dev_err(smmu_domain->smmu->dev, "failed to get runtime PM: 
>> %d\n", ret);
>> +        return -ENODEV;
>> +    }
>> +
>>       arm_smmu_write_context_bank(smmu_domain->smmu, cb->cfg->cbndx);
>>   +    pm_runtime_put_autosuspend(smmu_domain->smmu->dev);
>> +
>>       return 0;
>>   }
>>
>> ---
>> base-commit: 50c4a49f7292b33b454ea1a16c4f77d6965405dc
>> change-id: 20260210-qcom_smmu_pmfix-2aead2ba4e20
>>
>> Best regards,
>

Best regards,
-- 
Anna Maniscalco <anna.maniscalco2000@gmail.com>