Re: [PATCH] PCI/ATS: Disable ATS when ACS TB is set upstream

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Nov 05, 2026 at 05:04:12PM -0600, Bjorn Helgaas wrote:
>   * pci_dev_reset_iommu_prepare() vs pci_dev_reset_iommu_done()
> 
>       Different values will make gdev->reset_depth, group->recovery_cnt,
>       group->domain, and gdev->blocked get out of sync.
> 
>       I think it would be better if _iommu_prepare() and _iommu_done()
>       themselves tracked what _iommu_done() needs to do, for example
>       they could do something like this:
> 
>         int pci_dev_reset_iommu_prepare(struct pci_dev *pdev, bool *restore)
>         {
>             if (!pci_ats_supported(pdev) || !dev_has_iommu(&pdev->dev)) {
>                 *restore = false;
>                 return 0;
>             }
> 
>             *restore = true;
>             ...
>         }
> 
>       Then pci_dev_reset_iommu_done() wouldn't need to call
>       pci_ats_supported() or dev_has_iommu(), and users would look like
>       this:
> 
>         int pcie_flr(...)
>         {
>             bool restore;
> 
>             ret = pci_dev_reset_iommu_prepare(dev, &restore);
>             ...
>             if (restore)
>                 pci_dev_reset_iommu_done(dev);
>         }
> 
>       Or I guess we could call pci_dev_reset_iommu_done()
>       unconditionally and pass it 'restore' and it could test it

If the condition here is "an upstream bridge becomes inaccessible
during a reset", then the reset/flr itself fails?

The patch that you acked yesterday handles such a case:
https://lore.kernel.org/linux-iommu/20261105001312.GA1479227@bhelgaas/

Nicolin