linux-kernel - Re: [PATCH v5 2/6] iommu/qcom: Use the asid read from device-tree if specified

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Date:   Tue, 1 Aug 2023 14:49:54 +0100
From:   Will Deacon <will@...nel.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     agross@...nel.org, andersson@...nel.org, luca@...tu.xyz,
        konrad.dybcio@...aro.org, dmitry.baryshkov@...aro.org,
        joro@...tes.org, robin.murphy@....com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        robdclark@...il.com, linux-arm-msm@...r.kernel.org,
        iommu@...ts.linux.dev, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kernel@...labora.com,
        Marijn Suijten <marijn.suijten@...ainline.org>
Subject: Re: [PATCH v5 2/6] iommu/qcom: Use the asid read from device-tree if
 specified

On Thu, Jun 22, 2023 at 11:27:38AM +0200, AngeloGioacchino Del Regno wrote:
> As specified in this driver, the context banks are 0x1000 apart but
> on some SoCs the context number does not necessarily match this
> logic, hence we end up using the wrong ASID: keeping in mind that
> this IOMMU implementation relies heavily on SCM (TZ) calls, it is
> mandatory that we communicate the right context number.
> 
> Since this is all about how context banks are mapped in firmware,
> which may be board dependent (as a different firmware version may
> eventually change the expected context bank numbers), introduce a
> new property "qcom,ctx-asid": when found, the ASID will be forced
> as read from the devicetree.
> 
> When "qcom,ctx-asid" is not found, this driver retains the previous
> behavior as to avoid breaking older devicetrees or systems that do
> not require forcing ASID numbers.
> 
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> [Marijn: Rebased over next-20221111]
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>  drivers/iommu/arm/arm-smmu/qcom_iommu.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/qcom_iommu.c b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> index a503ed758ec3..8face57c4180 100644
> --- a/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> +++ b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> @@ -531,7 +531,8 @@ static int qcom_iommu_of_xlate(struct device *dev, struct of_phandle_args *args)
>  	 * index into qcom_iommu->ctxs:
>  	 */
>  	if (WARN_ON(asid < 1) ||
> -	    WARN_ON(asid > qcom_iommu->num_ctxs)) {
> +	    WARN_ON(asid > qcom_iommu->num_ctxs) ||
> +	    WARN_ON(qcom_iommu->ctxs[asid - 1] == NULL)) {
>  		put_device(&iommu_pdev->dev);
>  		return -EINVAL;
>  	}
> @@ -617,7 +618,8 @@ static int qcom_iommu_sec_ptbl_init(struct device *dev)
>  
>  static int get_asid(const struct device_node *np)
>  {
> -	u32 reg;
> +	u32 reg, val;
> +	int asid;
>  
>  	/* read the "reg" property directly to get the relative address
>  	 * of the context bank, and calculate the asid from that:
> @@ -625,7 +627,17 @@ static int get_asid(const struct device_node *np)
>  	if (of_property_read_u32_index(np, "reg", 0, &reg))
>  		return -ENODEV;
>  
> -	return reg / 0x1000;      /* context banks are 0x1000 apart */
> +	/*
> +	 * Context banks are 0x1000 apart but, in some cases, the ASID
> +	 * number doesn't match to this logic and needs to be passed
> +	 * from the DT configuration explicitly.
> +	 */
> +	if (!of_property_read_u32(np, "qcom,ctx-asid", &val))
> +		asid = val;
> +	else
> +		asid = reg / 0x1000;
> +
> +	return asid;

Shouldn't we at least have some error checking here? For example, ensuring
that the ASIDs are within range, aren't duplicates etc?

Also, can you elaborate a little more on what sort of ASID-to-Context
mappings you actually see in practice?

Will