[PATCH v5 1/2] iommu/arm-smmu-v3: Poll for CMD_SYNC outside cmdq lock

[robin.murphy@arm.com (Robin Murphy)]

On 18/10/18 11:55, John Garry wrote:
[...]
>> @@ -976,18 +1019,19 @@ static int __arm_smmu_cmdq_issue_sync(struct 
>> arm_smmu_device *smmu)
>> ?{
>> ???? u64 cmd[CMDQ_ENT_DWORDS];
>> ???? unsigned long flags;
>> -??? bool wfe = !!(smmu->features & ARM_SMMU_FEAT_SEV);
>> ???? struct arm_smmu_cmdq_ent ent = { .opcode = CMDQ_OP_CMD_SYNC };
>> -??? int ret;
>> +??? int sync_idx, sync_gen;
>>
>> ???? arm_smmu_cmdq_build_cmd(cmd, &ent);
>>
>> ???? spin_lock_irqsave(&smmu->cmdq.lock, flags);
>> -??? arm_smmu_cmdq_insert_cmd(smmu, cmd);
>> -??? ret = queue_poll_cons(&smmu->cmdq.q, true, wfe);
>> +??? if (smmu->prev_cmd_opcode != CMDQ_OP_CMD_SYNC)
>> +??????? arm_smmu_cmdq_insert_cmd(smmu, cmd);
> 
> Hi Robin,
> 
> If we did stop rebuilding the non-MSI command as I suggested, then we 
> would not have the case of building the command and then discarding it, 
> right?

I suppose so. But that build/discard case can also be avoided by 
applying patch 2/2 of this series ;)

Robin.

> 
> Thanks,
> John
> 
>> +??? sync_idx = smmu->cmdq.q.prod;
>> +??? sync_gen = READ_ONCE(smmu->cmdq_generation);
>> ???? spin_unlock_irqrestore(&smmu->cmdq.lock, flags);
>>
>> -??? return ret;
>> +??? return arm_smmu_sync_poll_cons(smmu, sync_idx, sync_gen);
>> ?}
>>
>> ?static void arm_smmu_cmdq_issue_sync(struct arm_smmu_device *smmu)
>>
> 
>