Re: [PATCH v3 04/12] iommu/vt-d: Move scalable mode ATS enablement to probe path

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2025/3/4 16:15, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@linux.intel.com>
>> Sent: Friday, February 28, 2025 5:26 PM
>>
>> Device ATS is currently enabled when a domain is attached to the device
>> and disabled when the domain is detached. This creates a limitation:
>> when the IOMMU is operating in scalable mode and IOPF is enabled, the
>> device's domain cannot be changed.
> could you extend it with your earlier reply?
> 
> https://lore.kernel.org/linux-iommu/6a418974-d06e-46e3-879f- 
> ab4c84a95231@linux.intel.com/
> 
>> -static void iommu_enable_pci_caps(struct device_domain_info *info)
>> +static void iommu_enable_pci_ats(struct device_domain_info *info)
>>   {
>>   	struct pci_dev *pdev;
>>
>> -	if (!dev_is_pci(info->dev))
>> +	if (!info->ats_supported)
>>   		return;
>>
>>   	pdev = to_pci_dev(info->dev);
>> -	if (info->ats_supported && pci_ats_page_aligned(pdev) &&
>> -	    !pci_enable_ats(pdev, VTD_PAGE_SHIFT))
>> +	if (!pci_ats_page_aligned(pdev))
>> +		return;
>> +
>> +	if (!pci_enable_ats(pdev, VTD_PAGE_SHIFT))
>>   		info->ats_enabled = 1;
>>   }
>>
> still prefer to some comment above as you explained in above
> reply. It's not obvious w/o knowing the tricky background.

Okay, sure.