linux-kernel - Re: [PATCH 1/2] perf/smmuv3: Don't reserve the register space that overlaps with the SMMUv3

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Date:   Wed, 20 Jan 2021 11:37:05 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
CC:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Neil Leeder <nleeder@...eaurora.org>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH 1/2] perf/smmuv3: Don't reserve the register space that
 overlaps with the SMMUv3



On 2021/1/19 20:32, Robin Murphy wrote:
> On 2021-01-19 01:59, Zhen Lei wrote:
>> Some SMMUv3 implementation embed the Perf Monitor Group Registers (PMCG)
>> inside the first 64kB region of the SMMU. Since SMMU and PMCG are managed
>> by two separate drivers, and this driver depends on ARM_SMMU_V3, so the
>> SMMU driver reserves the corresponding resource first, this driver should
>> not reserve the corresponding resource again. Otherwise, a resource
>> reservation conflict is reported during boot.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> ---
>>   drivers/perf/arm_smmuv3_pmu.c | 42 ++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 40 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/perf/arm_smmuv3_pmu.c b/drivers/perf/arm_smmuv3_pmu.c
>> index 74474bb322c3f26..dcce085431c6ce8 100644
>> --- a/drivers/perf/arm_smmuv3_pmu.c
>> +++ b/drivers/perf/arm_smmuv3_pmu.c
>> @@ -761,6 +761,44 @@ static void smmu_pmu_get_acpi_options(struct smmu_pmu *smmu_pmu)
>>       dev_notice(smmu_pmu->dev, "option mask 0x%x\n", smmu_pmu->options);
>>   }
>>   +static void __iomem *
>> +smmu_pmu_get_and_ioremap_resource(struct platform_device *pdev,
>> +                  unsigned int index,
>> +                  struct resource **out_res)
>> +{
>> +    int ret;
>> +    void __iomem *base;
>> +    struct resource *res;
>> +
>> +    res = platform_get_resource(pdev, IORESOURCE_MEM, index);
>> +    if (!res) {
>> +        dev_err(&pdev->dev, "invalid resource\n");
>> +        return IOMEM_ERR_PTR(-EINVAL);
>> +    }
>> +    if (out_res)
>> +        *out_res = res;
>> +
>> +    ret = region_intersects(res->start, resource_size(res),
>> +                IORESOURCE_MEM, IORES_DESC_NONE);
>> +    if (ret == REGION_INTERSECTS) {
>> +        /*
>> +         * The resource has already been reserved by the SMMUv3 driver.
>> +         * Don't reserve it again, just do devm_ioremap().
>> +         */
>> +        base = devm_ioremap(&pdev->dev, res->start, resource_size(res));
>> +    } else {
>> +        /*
>> +         * The resource may have not been reserved by any driver, or
>> +         * has been reserved but not type IORESOURCE_MEM. In the latter
>> +         * case, devm_ioremap_resource() reports a conflict and returns
>> +         * IOMEM_ERR_PTR(-EBUSY).
>> +         */
>> +        base = devm_ioremap_resource(&pdev->dev, res);
>> +    }
> 
> What if the PMCG driver simply happens to probe first?

There are 4 cases:
1) ARM_SMMU_V3=m, ARM_SMMU_V3_PMU=y
   It's not allowed. Becase: ARM_SMMU_V3_PMU depends on ARM_SMMU_V3
   config ARM_SMMU_V3_PMU
         tristate "ARM SMMUv3 Performance Monitors Extension"
         depends on ARM64 && ACPI && ARM_SMMU_V3

2) ARM_SMMU_V3=y, ARM_SMMU_V3_PMU=m
   No problem, SMMUv3 will be initialized first.

3) ARM_SMMU_V3=y, ARM_SMMU_V3_PMU=y
   vi drivers/Makefile
   60 obj-y                           += iommu/
   172 obj-$(CONFIG_PERF_EVENTS)       += perf/

   This link sequence ensure that SMMUv3 driver will be initialized first.
   They are currently at the same initialization level.

4) ARM_SMMU_V3=m, ARM_SMMU_V3_PMU=m
   Sorry, I thought module dependencies were generated based on "depends on".
   But I tried it today，module dependencies are generated only when symbol
   dependencies exist. I should use MODULE_SOFTDEP() to explicitly mark the
   dependency. I will send V2 later.


> 
> Robin.
> 
>> +
>> +    return base;
>> +}
>> +
>>   static int smmu_pmu_probe(struct platform_device *pdev)
>>   {
>>       struct smmu_pmu *smmu_pmu;
>> @@ -793,7 +831,7 @@ static int smmu_pmu_probe(struct platform_device *pdev)
>>           .capabilities    = PERF_PMU_CAP_NO_EXCLUDE,
>>       };
>>   -    smmu_pmu->reg_base = devm_platform_get_and_ioremap_resource(pdev, 0, &res_0);
>> +    smmu_pmu->reg_base = smmu_pmu_get_and_ioremap_resource(pdev, 0, &res_0);
>>       if (IS_ERR(smmu_pmu->reg_base))
>>           return PTR_ERR(smmu_pmu->reg_base);
>>   @@ -801,7 +839,7 @@ static int smmu_pmu_probe(struct platform_device *pdev)
>>         /* Determine if page 1 is present */
>>       if (cfgr & SMMU_PMCG_CFGR_RELOC_CTRS) {
>> -        smmu_pmu->reloc_base = devm_platform_ioremap_resource(pdev, 1);
>> +        smmu_pmu->reloc_base = smmu_pmu_get_and_ioremap_resource(pdev, 1, NULL);
>>           if (IS_ERR(smmu_pmu->reloc_base))
>>               return PTR_ERR(smmu_pmu->reloc_base);
>>       } else {
>>
> 
> .
>