On Thu, 2020-12-03 at 20:12 +0000, Verma, Vishal L wrote: > This is a public RFC of an ACPI proposal to add a new CXL Root Object > that indicates the presence of a CXL hierarchy. The proposal is being > made in the new 'Code First' workflow of the ACPI Spec Working Group. > The subject matter here has been explored in previously posted patches > to QEMU[1] as well as Linux[2]. These patches have served as a proof-of- > concept test vehicle to help ensure that the proposal works in practice. > The cover letter in series [2] goes into additional detail (section > titled 'ACPI0017') for the reasoning behind the proposal, and what is > needed beyond what's described in the CXL 2.0 spec. > > The change proposal that follows is in markdown format. > > [1]: https://lore.kernel.org/qemu-devel/20201111054724.794888-1-ben.widawsky@xxxxxxxxx/ > [2]: https://lore.kernel.org/linux-cxl/20201111054356.793390-1-ben.widawsky@xxxxxxxxx/ > > ---- > > # Title: Add CXL Root Object _HID > > # Status: Draft This ECR was approved in the ASWG today without any modifications, and this content can be expected to be present in the next release of the specification. > > # Document: ACPI Specification 6.4 > > # License > SPDX-License Identifier: CC-BY-4.0 > > # Submitter: > * Sponsor: Vishal Verma, Intel > * Creators/Contributors: > * Chet Douglas, Intel > * Ben Widawsky, Intel > * Dan Williams, Intel > * Vishal Verma, Intel > > # Summary of the Change > Add “Compute Express Link Root Object” enumeration value to the ACPI > Device IDs Table (5.160). > > # Benefits of the Change > Compute Express Link (CXL) is a new high-speed CPU-to-Device and CPU-to- > Memory interconnect. The new ACPI Device ID represents a singleton > device that allows the OSPM to trigger the enumeration of the CXL.mem > address space, and indicates the presence of cross Host Bridge > (ACPI0016) interleaved CXL.mem resources. > > # Impact of the Change > One new row added to the ACPI Device IDs table (5.160). > > # References > * Compute Express Link Specification v2.0, > <https://www.computeexpresslink.org/> > > # Detailed Description of the Change > > Add “Compute Express Link Root Object” enumeration device > > ### 5.6.7 Device Class-Specific Objects > > Most device objects are controlled through generic objects and ... > > Table 5.160 ACPI Device IDs > > > Value | Description | > > :--- | :---: | :---: | :--------------------------- | > > .. | .. | > > ACPI0017 | **Compute Express Link Root Object:** This device > represents the root of a CXL capable device hierarchy. It shall be > present whenever the platform allows OSPM to dynamically assign CXL > endpoints to a platform address space. | > > ## Special Instructions
