linux-kernel - Re: [PATCH v2 17/22] iommu/arm-smmu-v3-iommufd: Support implementation-defined hw

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Message-ID: <aBFIIJPmjIOecCMj@google.com>
Date: Tue, 29 Apr 2025 21:44:00 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, corbet@....net, will@...nel.org,
	bagasdotme@...il.com, robin.murphy@....com, joro@...tes.org,
	thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
	shuah@...nel.org, jsnitsel@...hat.com, nathan@...nel.org,
	peterz@...radead.org, yi.l.liu@...el.com, mshavit@...gle.com,
	zhangzekun11@...wei.com, iommu@...ts.linux.dev,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kselftest@...r.kernel.org, patches@...ts.linux.dev,
	mochs@...dia.com, alok.a.tiwari@...cle.com, vasant.hegde@....com
Subject: Re: [PATCH v2 17/22] iommu/arm-smmu-v3-iommufd: Support
 implementation-defined hw_info

On Fri, Apr 25, 2025 at 10:58:12PM -0700, Nicolin Chen wrote:
> Repurpose the @__reserved field in the struct iommu_hw_info_arm_smmuv3,
> to an HW implementation-defined field @impl.
> 
> This will be used by Tegra241 CMDQV implementation on top of a standard
> ARM SMMUv3 IOMMU. The @impl will be only valid if @flags is set with an
> implementation-defined flag.
> 
> Thus in the driver-level, add an hw_info impl op that will return such
> a flag to use the impl field.
> 
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>

Reviewed-by: Pranjal Shrivastava <praan@...gle.com>

> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h      |  1 +
>  include/uapi/linux/iommufd.h                     |  4 ++--
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c  | 16 +++++++++++++---
>  3 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> index a5835af72417..bab7a9ce1283 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -726,6 +726,7 @@ struct arm_smmu_impl_ops {
>  		struct arm_smmu_domain *smmu_domain, struct iommufd_ctx *ictx,
>  		unsigned int viommu_type,
>  		const struct iommu_user_data *user_data);
> +	u32 (*hw_info)(struct arm_smmu_device *smmu, u32 *impl);
>  };
>  
>  /* An SMMUv3 instance */
> diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
> index 06a763fda47f..b2614f0f1547 100644
> --- a/include/uapi/linux/iommufd.h
> +++ b/include/uapi/linux/iommufd.h
> @@ -554,7 +554,7 @@ struct iommu_hw_info_vtd {
>   *                                   (IOMMU_HW_INFO_TYPE_ARM_SMMUV3)
>   *
>   * @flags: Must be set to 0
> - * @__reserved: Must be 0
> + * @impl: Must be 0
>   * @idr: Implemented features for ARM SMMU Non-secure programming interface
>   * @iidr: Information about the implementation and implementer of ARM SMMU,
>   *        and architecture version supported
> @@ -585,7 +585,7 @@ struct iommu_hw_info_vtd {
>   */
>  struct iommu_hw_info_arm_smmuv3 {
>  	__u32 flags;
> -	__u32 __reserved;
> +	__u32 impl;
>  	__u32 idr[6];
>  	__u32 iidr;
>  	__u32 aidr;
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> index a8a78131702d..63861c60b615 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> @@ -10,7 +10,9 @@
>  void *arm_smmu_hw_info(struct device *dev, u32 *length, u32 *type)
>  {
>  	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> +	struct arm_smmu_device *smmu = master->smmu;
>  	struct iommu_hw_info_arm_smmuv3 *info;
> +	u32 flags = 0, impl = 0;
>  	u32 __iomem *base_idr;
>  	unsigned int i;
>  
> @@ -18,15 +20,23 @@ void *arm_smmu_hw_info(struct device *dev, u32 *length, u32 *type)
>  	if (!info)
>  		return ERR_PTR(-ENOMEM);
>  
> -	base_idr = master->smmu->base + ARM_SMMU_IDR0;
> +	base_idr = smmu->base + ARM_SMMU_IDR0;
>  	for (i = 0; i <= 5; i++)
>  		info->idr[i] = readl_relaxed(base_idr + i);
> -	info->iidr = readl_relaxed(master->smmu->base + ARM_SMMU_IIDR);
> -	info->aidr = readl_relaxed(master->smmu->base + ARM_SMMU_AIDR);
> +	info->iidr = readl_relaxed(smmu->base + ARM_SMMU_IIDR);
> +	info->aidr = readl_relaxed(smmu->base + ARM_SMMU_AIDR);
>  
>  	*length = sizeof(*info);
>  	*type = IOMMU_HW_INFO_TYPE_ARM_SMMUV3;
>  
> +	if (smmu->impl_ops && smmu->impl_ops->hw_info) {
> +		flags = smmu->impl_ops->hw_info(smmu, &impl);
> +		if (flags) {
> +			info->impl = impl;
> +			info->flags |= flags;
> +		}
> +	}
> +
>  	return info;
>  }
>  
> -- 
> 2.43.0
>