linux-kernel - Re: [PATCH v6 3/4] iommu/arm-smmu: Add global/context fault implementation hooks

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Date:   Tue, 23 Jun 2020 12:30:16 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Krishna Reddy <vdumpa@...dia.com>
Cc:     snikam@...dia.com, mperttunen@...dia.com, bhuntsman@...dia.com,
        will@...nel.org, joro@...tes.org, linux-kernel@...r.kernel.org,
        praithatha@...dia.com, talho@...dia.com,
        iommu@...ts.linux-foundation.org, nicolinc@...dia.com,
        linux-tegra@...r.kernel.org, yhsu@...dia.com, treding@...dia.com,
        linux-arm-kernel@...ts.infradead.org, bbiswas@...dia.com
Subject: Re: [PATCH v6 3/4] iommu/arm-smmu: Add global/context fault
 implementation hooks

On 2020-06-23 09:36, Thierry Reding wrote:
[...]
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 243bc4cb2705b..d720e1e191176 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -673,6 +673,7 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>>   	enum io_pgtable_fmt fmt;
>>   	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>>   	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
>> +	irqreturn_t (*context_fault)(int irq, void *dev);
>>   
>>   	mutex_lock(&smmu_domain->init_mutex);
>>   	if (smmu_domain->smmu)
>> @@ -835,7 +836,9 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>>   	 * handler seeing a half-initialised domain state.
>>   	 */
>>   	irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
>> -	ret = devm_request_irq(smmu->dev, irq, arm_smmu_context_fault,
>> +	context_fault = (smmu->impl && smmu->impl->context_fault) ?
>> +			 smmu->impl->context_fault : arm_smmu_context_fault;
> 
> A simpler way might have been to assign arm_smmu_context_fault to all
> implementations. That way we wouldn't have to perform this check here
> and instead just always using smmu->impl->context_fault.

But smmu->impl can still be NULL...

Everything in impl, including the presence of impl itself, is optional, 
so the notion of overriding a default with the same default doesn't 
really make much sense, and would go against the pattern everywhere else.

Robin.

>> +	ret = devm_request_irq(smmu->dev, irq, context_fault,
>>   			       IRQF_SHARED, "arm-smmu-context-fault", domain);
>>   	if (ret < 0) {
>>   		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
>> @@ -2107,6 +2110,7 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>>   	struct arm_smmu_device *smmu;
>>   	struct device *dev = &pdev->dev;
>>   	int num_irqs, i, err;
>> +	irqreturn_t (*global_fault)(int irq, void *dev);
>>   
>>   	smmu = devm_kzalloc(dev, sizeof(*smmu), GFP_KERNEL);
>>   	if (!smmu) {
>> @@ -2193,9 +2197,12 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>>   		smmu->num_context_irqs = smmu->num_context_banks;
>>   	}
>>   
>> +	global_fault = (smmu->impl && smmu->impl->global_fault) ?
>> +			smmu->impl->global_fault : arm_smmu_global_fault;
>> +
> 
> Same as above.
> 
> Thierry
>