Re: [Freedreno] [PATCH v2 2/7] iommu/arm-smmu: Add domain attribute for QCOM system cache

[Rob Clark]

On Thu, Jan 2, 2020 at 3:02 AM Sharat Masetty <smasetty@xxxxxxxxxxxxxx> wrote:
>
> From: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
>
> Add iommu domain attribute for using system cache aka last level
> cache on QCOM SoCs by client drivers like GPU to set right
> attributes for caching the hardware pagetables into the system cache.
>
> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
> Co-developed-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> ---
>  drivers/iommu/arm-smmu-qcom.c | 10 ++++++++++
>  drivers/iommu/arm-smmu.c      | 14 ++++++++++++++
>  drivers/iommu/arm-smmu.h      |  1 +
>  include/linux/iommu.h         |  1 +
>  4 files changed, 26 insertions(+)
>
> diff --git a/drivers/iommu/arm-smmu-qcom.c b/drivers/iommu/arm-smmu-qcom.c
> index 24c071c..d1d22df 100644
> --- a/drivers/iommu/arm-smmu-qcom.c
> +++ b/drivers/iommu/arm-smmu-qcom.c
> @@ -30,7 +30,17 @@ static int qcom_sdm845_smmu500_reset(struct arm_smmu_device *smmu)
>         return ret;
>  }
>
> +static int qcom_smmu_init_context(struct arm_smmu_domain *smmu_domain,
> +                                 struct io_pgtable_cfg *pgtbl_cfg)
> +{
> +       if (smmu_domain->sys_cache)
> +               pgtbl_cfg->coherent_walk = false;

just curious, does coherent walk not work with sys-cache, or is it
just that it is kind of pointless (given that, afaiu, the pagetables
can be cached by the system cache)?

> +
> +       return 0;
> +}
> +
>  static const struct arm_smmu_impl qcom_smmu_impl = {
> +       .init_context = qcom_smmu_init_context,
>         .reset = qcom_sdm845_smmu500_reset,
>  };
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 4f7e0c0..055b548 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1466,6 +1466,9 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>                 case DOMAIN_ATTR_NESTING:
>                         *(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
>                         return 0;
> +               case DOMAIN_ATTR_QCOM_SYS_CACHE:
> +                       *((int *)data) = smmu_domain->sys_cache;
> +                       return 0;
>                 default:
>                         return -ENODEV;
>                 }
> @@ -1506,6 +1509,17 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
>                         else
>                                 smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
>                         break;
> +               case DOMAIN_ATTR_QCOM_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-smmu.h b/drivers/iommu/arm-smmu.h
> index f57cdbe..8aeaaf0 100644
> --- a/drivers/iommu/arm-smmu.h
> +++ b/drivers/iommu/arm-smmu.h
> @@ -322,6 +322,7 @@ 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;
>  };
>
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 0c60e75..bd61c60 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -127,6 +127,7 @@ enum iommu_attr {
>         DOMAIN_ATTR_FSL_PAMUV1,
>         DOMAIN_ATTR_NESTING,    /* two stages of translation */
>         DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
> +       DOMAIN_ATTR_QCOM_SYS_CACHE,

Given that IOMMU_QCOM_SYS_CACHE was renamed to IOMMU_SYS_CACHE_ONLY, I
wonder if this domain attr should simply be DOMAIN_ATTR_SYS_CACHE?

But that said, the function of this domain attr seems to simply be to
disable coherent walk.. I wonder if naming the domain attr after what
it does would make more sense?

BR,
-R


>         DOMAIN_ATTR_MAX,
>  };
>
> --
> 1.9.1
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