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

[Baolu Lu]

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