linux-kernel - Re: [PATCH v7 5/6] iommu/arm-smmu-v3: Add support for non-strict mode

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Date:   Tue, 18 Sep 2018 20:09:45 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Will Deacon <will.deacon@....com>
Cc:     joro@...tes.org, thunder.leizhen@...wei.com,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, guohanjun@...wei.com, huawei.libin@...wei.com,
        john.garry@...wei.com
Subject: Re: [PATCH v7 5/6] iommu/arm-smmu-v3: Add support for non-strict mode

On 2018-09-18 6:10 PM, Will Deacon wrote:
> On Fri, Sep 14, 2018 at 03:30:23PM +0100, Robin Murphy wrote:
>> From: Zhen Lei <thunder.leizhen@...wei.com>
>>
>> Dynamically choose strict or non-strict mode for page table config based
>> on the iommu domain type.
> 
> It's the domain type in conjunction with the attribute that determines
> whether we use lazy or strict invalidation.
> 
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> [rm: convert to domain attribute]
>> Signed-off-by: Robin Murphy <robin.murphy@....com>
>> ---
>>   drivers/iommu/arm-smmu-v3.c | 30 ++++++++++++++++++++++++------
>>   1 file changed, 24 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index f10c852479fc..7bbfa5f7ce8e 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -612,6 +612,7 @@ struct arm_smmu_domain {
>>   	struct mutex			init_mutex; /* Protects smmu pointer */
>>   
>>   	struct io_pgtable_ops		*pgtbl_ops;
>> +	bool				non_strict;
>>   
>>   	enum arm_smmu_domain_stage	stage;
>>   	union {
>> @@ -1633,6 +1634,9 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
>>   	if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
>>   		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
>>   
>> +	if (smmu_domain->non_strict)
>> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
>> +
>>   	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
>>   	if (!pgtbl_ops)
>>   		return -ENOMEM;
>> @@ -1934,13 +1938,17 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>>   {
>>   	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>>   
>> -	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
>> -		return -EINVAL;
>> -
>>   	switch (attr) {
>>   	case DOMAIN_ATTR_NESTING:
>> +		if (domain->type != IOMMU_DOMAIN_UNMANAGED)
>> +			return -EINVAL;
>>   		*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
>>   		return 0;
>> +	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
>> +		if (domain->type != IOMMU_DOMAIN_DMA)
>> +			return -EINVAL;
>> +		*(int *)data = smmu_domain->non_strict;
>> +		return 0;
>>   	default:
>>   		return -ENODEV;
> 
> Hmm, there's a change in behaviour here (and also in the set function)
> which is that unknown attributes now return -ENODEV for managed domains
> instead of -EINVAL. I don't know if that's a problem, but I'd be inclined
> to switch on the domain type and then have a nested switch for the supported
> attributes.

Sure, a nested switch did actually cross my mind, but I was worried it 
might be a little boilerplate-heavy since there's still only one of each 
case (and this quick'n'dirty copy-paste job didn't need any thought...)

If that's your preference too, though, I'll respin both driver patches 
that way.

Robin.