linux-kernel - Re: [PATCH v3 2/6] iommu/qcom: Use the asid read from device-tree if specified

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Date:   Tue, 7 Mar 2023 17:47:32 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, agross@...nel.org
Cc:     andersson@...nel.org, joro@...tes.org, will@...nel.org,
        robin.murphy@....com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.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,
        marijn.suijten@...ainline.org, kernel@...labora.com,
        luca@...tu.xyz, a39.skl@...il.com, phone-devel@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v3 2/6] iommu/qcom: Use the asid read from device-tree if
 specified



On 7.03.2023 17:44, Dmitry Baryshkov wrote:
> On 15/11/2022 12:11, 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-num": when found, the ASID will be forced
>> as read from the devicetree.
>>
>> When "qcom,ctx-num" 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 bfd7b51eb5db..491a8093f3d6 100644
>> --- a/drivers/iommu/arm/arm-smmu/qcom_iommu.c
>> +++ b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
>> @@ -551,7 +551,8 @@ 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)) {
> 
> Separate change in my opinion. Please split it to a separate patch with proper Fixes: tag.
> 
>>           put_device(&iommu_pdev->dev);
>>           return -EINVAL;
>>       }
>> @@ -638,7 +639,8 @@ 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:
>> @@ -646,7 +648,17 @@ static int get_asid(const struct device_node *np)
>>       if (of_property_read_u32_index(np, "reg", 0, &reg))
Use platform_get_resource(pdev, IORESOURCE_MEM, 0); reg = res->start
or something like this, the current approach relies on #address-cells = <1>

Konrad
>>           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-num", &val))
>> +        asid = reg / 0x1000;
>> +    else
>> +        asid = val;
> 
> As a matter of preference (and logic) I'd have written that as:
> 
> if (!of_property_read(np, "qcom,ctx-num", &val))
>     asid = val;
> else
>     asid = reg / 0x1000;
> 
> LGTM otherwise
> 
>> +
>> +    return asid;
>>   }
>>     static int qcom_iommu_ctx_probe(struct platform_device *pdev)
>