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1Introduction2============3 4The FPGA subsystem supports reprogramming FPGAs dynamically under5Linux. 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 and10 enumeration) from lower layers that know how to program a specific11 FPGA.12 13* Code should not be shared between upper and lower layers. This14 should go without saying. If that seems necessary, there's probably15 framework functionality that can be added that will benefit16 other users. Write the linux-fpga mailing list and maintainers and17 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 Manager24------------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 contain28the knowledge of how to program a specific device. This subsystem29includes the framework in fpga-mgr.c and the low level drivers that30are registered with it.31 32FPGA Bridge33-----------34 35FPGA Bridges prevent spurious signals from going out of an FPGA or a36region of an FPGA during programming. They are disabled before37programming begins and re-enabled afterwards. An FPGA bridge may be38actual hard hardware that gates a bus to a CPU or a soft ("freeze")39bridge in FPGA fabric that surrounds a partial reconfiguration region40of an FPGA. This subsystem includes fpga-bridge.c and the low level41drivers that are registered with it.42 43FPGA Region44-----------45 46If you are adding a new interface to the FPGA framework, add it on top47of an FPGA region.48 49The FPGA Region framework (fpga-region.c) associates managers and50bridges as reconfigurable regions. A region may refer to the whole51FPGA in full reconfiguration or to a partial reconfiguration region.52 53The Device Tree FPGA Region support (of-fpga-region.c) handles54reprogramming FPGAs when device tree overlays are applied.55