linux-kernel - Re: [PATCH v12 04/13] iommu: Add a domain attribute to get/set a pagetable configuration

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Date:   Thu, 13 Aug 2020 14:14:12 +0100
From:   Will Deacon <will@...nel.org>
To:     Jordan Crouse <jcrouse@...eaurora.org>
Cc:     linux-arm-msm@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        iommu@...ts.linux-foundation.org, freedreno@...ts.freedesktop.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 04/13] iommu: Add a domain attribute to get/set a
 pagetable configuration

On Mon, Aug 10, 2020 at 04:26:48PM -0600, Jordan Crouse wrote:
> Add domain attribute DOMAIN_ATTR_PGTABLE_CFG. This will be used by
> arm-smmu to share the current pagetable configuration with the
> leaf driver and to allow the leaf driver to set up a new pagetable
> configuration under certain circumstances.
> 
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
> 
>  include/linux/iommu.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index fee209efb756..995ab8c47ef2 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_PGTABLE_CFG,
>  	DOMAIN_ATTR_MAX,
>  };

Nobody other than the adreno gpu uses this, so can we avoid exposing it
in the IOMMU API, please? Given that you have a reference to the adreno
GPU device in the SMMU implementation code thanks to .alloc_context_bank(),
can you squirrel some function pointers away in the driver data (i.e. with
dev_set_drvdata()) instead?

Will