Subject: [PATCH] iommu/arm-smmu: Don't allocate resources for bypass domains

From: [email-masked] (Eric Auger)
Date: Fri, 15 Apr 2016 17:11:28 +0200

Hi Will,
On 04/15/2016 03:05 PM, Will Deacon wrote:
> On Wed, Apr 13, 2016 at 03:46:57PM +0100, Robin Murphy wrote:
>> Until we get fully plumbed into of_iommu_configure, our default
>> IOMMU_DOMAIN_DMA domains just bypass translation. Since we achieve that
>> by leaving the stream table entries set to bypass instead of pointing at
>> a translation context, the context bank we allocate for the domain is
>> completely wasted. Context banks are typically a rather limited
>> resource, so don't hog ones we don't need.
> 
> Eric, does this resolve your remaining passthrough regressions when applied
> on top of my patch?

Yes it does. Thank you for the fixes.

Best Regards

Eric
> 
> Will
> 
>> Reported-by: Eric Auger <[email-masked]>
>> Signed-off-by: Robin Murphy <[email-masked]>
>> ---
>>  drivers/iommu/arm-smmu.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 5158feb..7c39ac4 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -826,6 +826,12 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>>  	if (smmu_domain->smmu)
>>  		goto out_unlock;
>>  
>> +	/* We're bypassing these SIDs, so don't allocate an actual context */
>> +	if (domain->type == IOMMU_DOMAIN_DMA) {
>> +		smmu_domain->smmu = smmu;
>> +		goto out_unlock;
>> +	}
>> +
>>  	/*
>>  	 * Mapping the requested stage onto what we support is surprisingly
>>  	 * complicated, mainly because the spec allows S1+S2 SMMUs without
>> @@ -948,7 +954,7 @@ static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
>>  	void __iomem *cb_base;
>>  	int irq;
>>  
>> -	if (!smmu)
>> +	if (!smmu || domain->type == IOMMU_DOMAIN_DMA)
>>  		return;
>>  
>>  	/*
>> -- 
>> 2.7.3.dirty
>>