Re: [PATCH v3 3/6] iommu/qcom: Properly reset the IOMMU context

[Dmitry Baryshkov]

On 15/11/2022 12:11, AngeloGioacchino Del Regno wrote:
> Avoid context faults by resetting the context(s) entirely at
> detach_dev() time and also do the same before programming the
> context for domain initialization.
>
> Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
> [Marijn: Rebased over next-20221111]
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>

Probably:
Fixes: 0ae349a0f33f ("iommu/qcom: Add qcom_iommu")

What causes context faults? Shouldn't the context be disabled once we 
write 0 to CB_SCTLR?

> ---
>   drivers/iommu/arm/arm-smmu/qcom_iommu.c | 20 ++++++++++++++++++--
>   1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iommu/arm/arm-smmu/qcom_iommu.c b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> index 491a8093f3d6..49f4308f1bd2 100644
> --- a/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> +++ b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> @@ -223,6 +223,20 @@ static irqreturn_t qcom_iommu_fault(int irq, void *dev)
>   	return IRQ_HANDLED;
>   }
>   
> +static void qcom_iommu_reset_ctx(struct qcom_iommu_ctx *ctx)
> +{
> +	iommu_writel(ctx, ARM_SMMU_CB_FAR, 0);
> +	iommu_writel(ctx, ARM_SMMU_CB_FSR, ARM_SMMU_FSR_FAULT);
> +	iommu_writel(ctx, ARM_SMMU_CB_S1_MAIR1, 0);
> +	iommu_writel(ctx, ARM_SMMU_CB_PAR, 0);
> +	iommu_writel(ctx, ARM_SMMU_CB_S1_MAIR0, 0);
> +	iommu_writel(ctx, ARM_SMMU_CB_SCTLR, 0);
> +	iommu_writel(ctx, ARM_SMMU_CB_TCR2, 0);
> +	iommu_writel(ctx, ARM_SMMU_CB_TCR, 0);
> +	iommu_writeq(ctx, ARM_SMMU_CB_TTBR0, 0);
> +	iommu_writeq(ctx, ARM_SMMU_CB_TTBR1, 0);
> +}
> +
>   static int qcom_iommu_init_domain(struct iommu_domain *domain,
>   				  struct qcom_iommu_dev *qcom_iommu,
>   				  struct device *dev)
> @@ -273,6 +287,8 @@ static int qcom_iommu_init_domain(struct iommu_domain *domain,
>   			ctx->secure_init = true;
>   		}
>   
> +		qcom_iommu_reset_ctx(ctx);

Is it enough to write 0 to ARM_SMMU_CB_SCTLR here instead of doing the 
full reset?

> +
>   		/* TTBRs */
>   		iommu_writeq(ctx, ARM_SMMU_CB_TTBR0,
>   				pgtbl_cfg.arm_lpae_s1_cfg.ttbr |
> @@ -401,8 +417,8 @@ static void qcom_iommu_detach_dev(struct iommu_domain *domain, struct device *de
>   	for (i = 0; i < fwspec->num_ids; i++) {
>   		struct qcom_iommu_ctx *ctx = to_ctx(qcom_domain, fwspec->ids[i]);
>   
> -		/* Disable the context bank: */
> -		iommu_writel(ctx, ARM_SMMU_CB_SCTLR, 0);
> +		/* Disable and reset the context bank */
> +		qcom_iommu_reset_ctx(ctx);
>   
>   		ctx->domain = NULL;
>   	}

--
With best wishes
Dmitry