Re: [PATCH v8 1/3] iommu/arm-smmu: add NVIDIA implementation for dual ARM MMU-500 usage

[Jon Hunter]

On 30/06/2020 17:32, Jon Hunter wrote:
> On 30/06/2020 17:23, Krishna Reddy wrote:
>>>> +struct arm_smmu_device *nvidia_smmu_impl_init(struct arm_smmu_device 
>>>> +*smmu) {
>>>> +	unsigned int i;
>> ....
>>>> +	for (i = 1; i < MAX_SMMU_INSTANCES; i++) {
>>>> +		struct resource *res;
>>>> +
>>>> +		res = platform_get_resource(pdev, IORESOURCE_MEM, i);
>>>> +		if (!res)
>>>> +			break;
>>
>>> Currently this driver is only supported for Tegra194 which I understand has 3 SMMUs. Therefore, I don't feel that we should fail silently here, I think it is better to return an error if all 3 cannot be initialised.
>>
>> Initialization of all the three SMMU instances is not necessary here.
> 
> That is not what I am saying.
> 
>> The driver can work with all the possible number of instances 1, 2 and 3 based on the DT config though it doesn't make much sense to use it with 1 instance.
>> There is no silent failure here from driver point of view. If there is misconfig in DT, SMMU faults would catch issues.
> 
> I disagree and you should return a proper error here.

OK, well I see what you are saying, but if we intended to support all 3
for Tegra194, then we should ensure all 3 are initialised correctly.

My concern here is testing, because when things break in upstream I am
usually the one that tracks it down. Not having clear warning/error
messages when something is not initialised as expected makes it harder.

It would be better to query the number of SMMUs populated in device-tree
and then ensure that all are initialised correctly.

Jon

-- 
nvpublic