1Introduction 2============ 3 4The FPGA subsystem supports reprogramming FPGAs dynamically under 5Linux. Some of the core intentions of the FPGA subsystems are: 6 7* The FPGA subsystem is vendor agnostic. 8 9* The FPGA subsystem separates upper layers (userspace interfaces and 10 enumeration) from lower layers that know how to program a specific 11 FPGA. 12 13* Code should not be shared between upper and lower layers. This 14 should go without saying. If that seems necessary, there's probably 15 framework functionality that can be added that will benefit 16 other users. Write the linux-fpga mailing list and maintainers and 17 seek out a solution that expands the framework for broad reuse. 18 19* Generally, when adding code, think of the future. Plan for reuse. 20 21The framework in the kernel is divided into: 22 23FPGA Manager 24------------ 25 26If you are adding a new FPGA or a new method of programming an FPGA, 27this is the subsystem for you. Low level FPGA manager drivers contain 28the knowledge of how to program a specific device. This subsystem 29includes the framework in fpga-mgr.c and the low level drivers that 30are registered with it. 31 32FPGA Bridge 33----------- 34 35FPGA Bridges prevent spurious signals from going out of an FPGA or a 36region of an FPGA during programming. They are disabled before 37programming begins and re-enabled afterwards. An FPGA bridge may be 38actual hard hardware that gates a bus to a CPU or a soft ("freeze") 39bridge in FPGA fabric that surrounds a partial reconfiguration region 40of an FPGA. This subsystem includes fpga-bridge.c and the low level 41drivers that are registered with it. 42 43FPGA Region 44----------- 45 46If you are adding a new interface to the FPGA framework, add it on top 47of an FPGA region. 48 49The FPGA Region framework (fpga-region.c) associates managers and 50bridges as reconfigurable regions. A region may refer to the whole 51FPGA in full reconfiguration or to a partial reconfiguration region. 52 53The Device Tree FPGA Region support (of-fpga-region.c) handles 54reprogramming FPGAs when device tree overlays are applied. 55