AMD CDX Being Prepared For Linux As The Bus Between Future APUs & FPGAs

Written by Michael Larabel in AMD on 17 January 2023 at 11:14 AM EST. 11 Comments
After quietly posting a "request for comments" patch series a few months back to no fanfare, AMD today published their post-RFC patch series today for introducing the AMD CDX bus to the Linux kernel. AMD CDX is ultimately for the interface/bus between the APU and FPGA(s) with future hardware.

There has long been rumors, patent filings, and other material over AMD's prospects for embedding FPGAs into APUs. Things have obviously heated up and more indications emerged since AMD's acquisition of Xilinx. In preparation for future APUs with FPGAs, AMD is in the process of introducing the CDX bus to the Linux kernel as what will be the interface for interacting with the FPGAs.

AMD CDX bus overview.

The CPU cores can interact with the FPGA hardware devices using a memory-mapped interface exposed by the firmware. The CDX bus is designed to be able to support multiple FPGA hardware devices.
Introduces AMD CDX bus, which provides a mechanism to discover/rescan CDX devices. The CDX devices are memory mapped on system bus for embedded CPUs.

CDX controller interacts with the firmware to query different CDX devices present in the Fabric and expose them to the Linux host on CDX bus.

This patch series:
- Introduces the CDX bus and CDX devices.
- Device tree binding for CDX controller
- Support for CDX bus in arm-smmu-v3 driver
- Add MCDI (Management CPU Driver Interface) as a protocol for communication with RPU Firmware
- Support RPMSg channel for Firmware communication

See this patch series for AMD's work on the CDX bus support for the Linux kernel. This work is now undergoing review before its eventual mainlining, which will hopefully all be squared away before AMD introduces any new products featuring integrated FPGAs using the CDX bus.
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