Subject: Re: [PATCHv7 2/7] iommu/arm-smmu: Add domain attribute for system cache

From: Sai Prakash Ranjan <[email-masked]>
Date: Wed, 11 Nov 2020 12:10:50 +0530

On 2020-11-10 17:48, Will Deacon wrote:
> On Fri, Oct 30, 2020 at 02:53:09PM +0530, Sai Prakash Ranjan wrote:
>> Add iommu domain attribute for using system cache aka last level
>> cache by client drivers like GPU to set right attributes for caching
>> the hardware pagetables into the system cache.
>> 
>> Signed-off-by: Sai Prakash Ranjan <[email-masked]>
>> ---
>>  drivers/iommu/arm/arm-smmu/arm-smmu.c | 17 +++++++++++++++++
>>  drivers/iommu/arm/arm-smmu/arm-smmu.h |  1 +
>>  include/linux/iommu.h                 |  1 +
>>  3 files changed, 19 insertions(+)
>> 
>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c 
>> b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> index b1cf8f0abc29..070d13f80c7e 100644
>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> @@ -789,6 +789,9 @@ static int arm_smmu_init_domain_context(struct 
>> iommu_domain *domain,
>>  	if (smmu_domain->non_strict)
>>  		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
>> 
>> +	if (smmu_domain->sys_cache)
>> +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_SYS_CACHE;
>> +
>>  	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
>>  	if (!pgtbl_ops) {
>>  		ret = -ENOMEM;
>> @@ -1520,6 +1523,9 @@ static int arm_smmu_domain_get_attr(struct 
>> iommu_domain *domain,
>>  		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
>>  			*(int *)data = smmu_domain->non_strict;
>>  			return 0;
>> +		case DOMAIN_ATTR_SYS_CACHE:
>> +			*((int *)data) = smmu_domain->sys_cache;
>> +			return 0;
>>  		default:
>>  			return -ENODEV;
>>  		}
>> @@ -1551,6 +1557,17 @@ static int arm_smmu_domain_set_attr(struct 
>> iommu_domain *domain,
>>  			else
>>  				smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
>>  			break;
>> +		case DOMAIN_ATTR_SYS_CACHE:
>> +			if (smmu_domain->smmu) {
>> +				ret = -EPERM;
>> +				goto out_unlock;
>> +			}
>> +
>> +			if (*((int *)data))
>> +				smmu_domain->sys_cache = true;
>> +			else
>> +				smmu_domain->sys_cache = false;
>> +			break;
>>  		default:
>>  			ret = -ENODEV;
>>  		}
>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h 
>> b/drivers/iommu/arm/arm-smmu/arm-smmu.h
>> index 885840f3bec8..dfc44d806671 100644
>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
>> @@ -373,6 +373,7 @@ struct arm_smmu_domain {
>>  	struct mutex			init_mutex; /* Protects smmu pointer */
>>  	spinlock_t			cb_lock; /* Serialises ATS1* ops and TLB syncs */
>>  	struct iommu_domain		domain;
>> +	bool				sys_cache;
>>  };
>> 
>>  struct arm_smmu_master_cfg {
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index b95a6f8db6ff..4f4bb9c6f8f6 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -118,6 +118,7 @@ enum iommu_attr {
>>  	DOMAIN_ATTR_FSL_PAMUV1,
>>  	DOMAIN_ATTR_NESTING,	/* two stages of translation */
>>  	DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
>> +	DOMAIN_ATTR_SYS_CACHE,
> 
> I think you're trying to make this look generic, but it's really not.
> If we need to funnel io-pgtable quirks through domain attributes, then 
> I
> think we should be open about that and add something like
> DOMAIN_ATTR_IO_PGTABLE_CFG which could take a struct of page-table
> configuration data for the domain (this could just be quirks initially,
> but maybe it's worth extending to take ias, oas and page size)
> 

Actually the initial versions used DOMAIN_ATTR_QCOM_SYS_CACHE
to make it QCOM specific and not generic, I don't see anyone else
using this attribute, would that work?

Thanks,
Sai

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