[RFC PATCH 04/30] iommu/arm-smmu-v3: Add support for PCI ATS

[Jean-Philippe Brucker]

On 03/04/17 09:34, Sunil Kovvuri wrote:
>> +static size_t arm_smmu_atc_invalidate_domain(struct arm_smmu_domain *smmu_domain,
>> +                                            unsigned long iova, size_t size)
>> +{
>> +       unsigned long flags;
>> +       struct arm_smmu_cmdq_ent cmd = {0};
>> +       struct arm_smmu_group *smmu_group;
>> +       struct arm_smmu_master_data *master;
>> +       struct arm_smmu_device *smmu = smmu_domain->smmu;
>> +       struct arm_smmu_cmdq_ent sync_cmd = {
>> +               .opcode = CMDQ_OP_CMD_SYNC,
>> +       };
>> +
>> +       spin_lock_irqsave(&smmu_domain->groups_lock, flags);
>> +
>> +       list_for_each_entry(smmu_group, &smmu_domain->groups, domain_head) {
>> +               if (!smmu_group->ats_enabled)
>> +                       continue;
> 
> If ATS is not supported, this seems to increase no of cycles spent in
> pgtbl_lock.
> Can we return from this API by checking 'ARM_SMMU_FEAT_ATS' in smmu->features ?

Sure, I can add a check before taking the lock. Have you been able to
observe a significant difference in cycles between checking FEAT_ATS,
checking group->ats_enabled after taking the lock, and removing this
function call altogether?

Thanks,
Jean-Philippe