Re: [RFC] Proposal: Add sysfs interface for PCIe TPH Steering Tag retrieval and configuration

Jason Gunthorpe
2026-04-14T15:11:27Z

On Tue, Apr 14, 2026 at 10:46:00PM +0800, fengchengwen wrote:
> We have a real platform requirement:
>
> * 1. Devices in TPH Device-Specific Mode with no standard ST table
> * 2. Steering Tags must be obtained from ACPI _DSM (kernel-only)
> * 3. Devices are fully managed by userspace drivers (VFIO/UIO)
> * 4. Userspace must program STs into vendor-specific registers

No, this is nonsenscial too.

If you want to control the steering tags for MMIO BAR memory exposed
by VFIO then the DMABUF mechanism Keith & co has been working on is
the correct approach.

If the VFIO user needs to control steering tags for the device it is
directly controling then it must do that through VFIO ioctls.

Nobody messes around with other devices under the covers of the
operating kernel driver. Stop proposing that.

Jason