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

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Message-ID: <BN9PR11MB52768462B8DDFBAB1EDE02C28CC82@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 4 Mar 2025 08:15:50 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, "Will
 Deacon" <will@...nel.org>, Robin Murphy <robin.murphy@....com>, "Jason
 Gunthorpe" <jgg@...pe.ca>
CC: "Jiang, Dave" <dave.jiang@...el.com>, Vinod Koul <vkoul@...nel.org>,
	Fenghua Yu <fenghuay@...dia.com>, Zhangfei Gao <zhangfei.gao@...aro.org>,
	Zhou Wang <wangzhou1@...ilicon.com>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 04/12] iommu/vt-d: Move scalable mode ATS enablement to
 probe path

> From: Lu Baolu <baolu.lu@...ux.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.