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

From: Sai Prakash Ranjan <[email-masked]>
Date: Sat, 14 Nov 2020 17:17:09 +0530

On 2020-11-12 15:05, Will Deacon wrote:
> On Wed, Nov 11, 2020 at 12:10:50PM +0530, Sai Prakash Ranjan wrote:
>> 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?
> 
> No -- I'd prefer to have _one_ domain attribute for funneling all the
> IP_PGTABLE_CFG data. Otherwise, we'll just end up with things like
> DOMAIN_ATTR_QCOM_SYS_CACHE_EXT or DOMAIN_ATTR_QCOM_QUIRKS later on.
> 

Right, that makes sense. I will add this in next version.

Thanks,
Sai

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