Re: [PATCH 2/2] iommu/vt-d: Remove hardware automatic ATS dependency

From: Baolu Lu
Date: Mon Jun 24 2024 - 04:11:38 EST


On 2024/6/24 16:06, Yi Liu wrote:
On 2024/6/24 13:25, Lu Baolu wrote:
If a device is listed in the SATC table with ATC_REQUIRED flag set, it
indicates that the device has a functional requirement to enable its ATC
(via the ATS capability) for device operation. However, when IOMMU is
running in the legacy mode, ATS could be automatically supported by the
hardware so that the OS has no need to support the ATS functionality.

It seems like if VT-d hw is operating in legacy mode, ATS is enabled
automatically?

Yes.

This is really suprising. Maybe I got it wrongly. Could you
elaborate a bit?

It's for backward compatible purpose, but I have no hardware details.

Best regards,
baolu