linux-kernel - Re: [PATCH v9 4/7] iommu/arm-smmu: Add a pointer to the attached device to smmu

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Date:   Mon, 13 Jul 2020 16:09:02 +0100
From:   Will Deacon <will@...nel.org>
To:     Jordan Crouse <jcrouse@...eaurora.org>
Cc:     linux-arm-msm@...r.kernel.org,
        John Stultz <john.stultz@...aro.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        freedreno@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 4/7] iommu/arm-smmu: Add a pointer to the attached
 device to smmu_domain

On Fri, Jun 26, 2020 at 02:00:38PM -0600, Jordan Crouse wrote:
> Add a link to the pointer to the struct device that is attached to a
> domain. This makes it easy to get the pointer if it is needed in the
> implementation specific code.
> 
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
> 
>  drivers/iommu/arm-smmu.c | 6 ++++--
>  drivers/iommu/arm-smmu.h | 1 +
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 048de2681670..060139452c54 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -668,7 +668,8 @@ static void arm_smmu_write_context_bank(struct arm_smmu_device *smmu, int idx)
>  }
>  
>  static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> -					struct arm_smmu_device *smmu)
> +					struct arm_smmu_device *smmu,
> +					struct device *dev)
>  {
>  	int irq, start, ret = 0;
>  	unsigned long ias, oas;
> @@ -801,6 +802,7 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  		cfg->asid = cfg->cbndx;
>  
>  	smmu_domain->smmu = smmu;
> +	smmu_domain->dev = dev;
>  
>  	pgtbl_cfg = (struct io_pgtable_cfg) {
>  		.pgsize_bitmap	= smmu->pgsize_bitmap,
> @@ -1190,7 +1192,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>  		return ret;
>  
>  	/* Ensure that the domain is finalised */
> -	ret = arm_smmu_init_domain_context(domain, smmu);
> +	ret = arm_smmu_init_domain_context(domain, smmu, dev);
>  	if (ret < 0)
>  		goto rpm_put;
>  
> diff --git a/drivers/iommu/arm-smmu.h b/drivers/iommu/arm-smmu.h
> index 5f2de20e883b..d33cfe26b2f5 100644
> --- a/drivers/iommu/arm-smmu.h
> +++ b/drivers/iommu/arm-smmu.h
> @@ -345,6 +345,7 @@ 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;
> +	struct device			*dev;	/* Device attached to this domain */

This really doesn't feel right to me -- you can generally have multiple
devices attached to a domain and they can come and go without the domain
being destroyed. Perhaps you could instead identify the GPU during
cfg_probe() and squirrel that information away somewhere?

The rest of the series looks ok to me.

Will