linux-kernel - Re: [PATCH v18 2/4] iommu/arm-smmu: Add a way for implementations to influence SCTLR

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Message-ID: <0a00c162-ad77-46b7-85ad-e11229b57a3d@arm.com>
Date:   Mon, 2 Nov 2020 18:18:45 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Jordan Crouse <jcrouse@...eaurora.org>,
        linux-arm-msm@...r.kernel.org
Cc:     iommu@...ts.linux-foundation.org, Will Deacon <will@...nel.org>,
        Rob Clark <robdclark@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Krishna Reddy <vdumpa@...dia.com>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Thierry Reding <treding@...dia.com>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v18 2/4] iommu/arm-smmu: Add a way for implementations to
 influence SCTLR

On 2020-11-02 17:14, Jordan Crouse wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> For the Adreno GPU's SMMU, we want SCTLR.HUPCF set to ensure that
> pending translations are not terminated on iova fault.  Otherwise
> a terminated CP read could hang the GPU by returning invalid
> command-stream data.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
> 
>   drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 6 ++++++
>   drivers/iommu/arm/arm-smmu/arm-smmu.c      | 3 +++
>   drivers/iommu/arm/arm-smmu/arm-smmu.h      | 3 +++
>   3 files changed, 12 insertions(+)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> index 1e942eed2dfc..0663d7d26908 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> @@ -129,6 +129,12 @@ static int qcom_adreno_smmu_init_context(struct arm_smmu_domain *smmu_domain,
>   	    (smmu_domain->cfg.fmt == ARM_SMMU_CTX_FMT_AARCH64))
>   		pgtbl_cfg->quirks |= IO_PGTABLE_QUIRK_ARM_TTBR1;
>   
> +	/*
> +	 * On the GPU device we want to process subsequent transactions after a
> +	 * fault to keep the GPU from hanging
> +	 */
> +	smmu_domain->cfg.sctlr_set |= ARM_SMMU_SCTLR_HUPCF;
> +
>   	/*
>   	 * Initialize private interface with GPU:
>   	 */
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> index dad7fa86fbd4..1f06ab219819 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> @@ -617,6 +617,9 @@ void arm_smmu_write_context_bank(struct arm_smmu_device *smmu, int idx)
>   	if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
>   		reg |= ARM_SMMU_SCTLR_E;
>   
> +	reg |= cfg->sctlr_set;
> +	reg &= ~cfg->sctlr_clr;

Since we now have a write_s2cr hook, I'm inclined to think that the 
consistency of a write_sctlr hook that could similarly apply its own 
arbitrary tweaks would make sense for this. Does anyone have any strong 
opinions?

Robin.

> +
>   	arm_smmu_cb_write(smmu, idx, ARM_SMMU_CB_SCTLR, reg);
>   }
>   
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> index 6c5ff9999eae..ddf2ca4c923d 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> @@ -144,6 +144,7 @@ enum arm_smmu_cbar_type {
>   #define ARM_SMMU_CB_SCTLR		0x0
>   #define ARM_SMMU_SCTLR_S1_ASIDPNE	BIT(12)
>   #define ARM_SMMU_SCTLR_CFCFG		BIT(7)
> +#define ARM_SMMU_SCTLR_HUPCF		BIT(8)
>   #define ARM_SMMU_SCTLR_CFIE		BIT(6)
>   #define ARM_SMMU_SCTLR_CFRE		BIT(5)
>   #define ARM_SMMU_SCTLR_E		BIT(4)
> @@ -341,6 +342,8 @@ struct arm_smmu_cfg {
>   		u16			asid;
>   		u16			vmid;
>   	};
> +	u32				sctlr_set;    /* extra bits to set in SCTLR */
> +	u32				sctlr_clr;    /* bits to mask in SCTLR */
>   	enum arm_smmu_cbar_type		cbar;
>   	enum arm_smmu_context_fmt	fmt;
>   };
>