Hi Lu,
Tested this on an X1 Carbon G12 with a kernel built form drm-tip and this patch - and was able to boot successfully with pci=noats
Tested-by: Mark Pearson <mpearson-lenovo@xxxxxxxxx>
Mark
PS - note on small typo below.
On Wed, Sep 4, 2024, at 2:07 AM, Lu Baolu wrote:
> SOC-integrated devices on some platforms require their PCI ATS enabled
> for operation when the IOMMU is in scalable mode. Those devices are
> reported via ACPI/SATC table with the ATC_REQUIRED bit set in the Flags
> field.
>
> The PCI subsystem offers the 'pci=noats' kernel command to disable PCI
> ATS on all devices. Using 'pci=noat' with devices that require PCI ATS
pci=noats
> can cause a conflict, leading to boot failure, especially if the device
> is a graphics device.
>
> To prevent this issue, check PCI ATS support before enumerating the IOMMU
> devices. If any device requires PCI ATS, but PCI ATS is disabled by
> 'pci=noats', switch the IOMMU to operate in legacy mode to ensure
> successful booting.
>
> Fixes: 97f2f2c5317f ("iommu/vt-d: Enable ATS for the devices in SATC table")
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12036
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
> drivers/iommu/intel/iommu.c | 22 +++++++++++++++++++---
> 1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 4aa070cf56e7..8f275e046e91 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -3127,10 +3127,26 @@ int dmar_iommu_notify_scope_dev(struct
> dmar_pci_notify_info *info)
> (void *)satc + satc->header.length,
> satc->segment, satcu->devices,
> satcu->devices_cnt);
> - if (ret > 0)
> - break;
> - else if (ret < 0)
> + if (ret < 0)
> return ret;
> +
> + if (ret > 0) {
> + /*
> + * The device requires PCI/ATS when the IOMMU
> + * works in the scalable mode. If PCI/ATS is
> + * disabled using the pci=noats kernel parameter,
> + * the IOMMU will default to legacy mode. Users
> + * are informed of this change.
> + */
> + if (intel_iommu_sm && satcu->atc_required &&
> + !pci_ats_supported(info->dev)) {
> + pci_warn(info->dev,
> + "PCI/ATS not supported, system working in IOMMU legacy mode\n");
> + intel_iommu_sm = 0;
> + }
> +
> + break;
> + }
> } else if (info->event == BUS_NOTIFY_REMOVED_DEVICE) {
> if (dmar_remove_dev_scope(info, satc->segment,
> satcu->devices, satcu->devices_cnt))
> --
> 2.34.1
