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Commit 66c472cd authored by Alan Tull's avatar Alan Tull Committed by Greg Kroah-Hartman
Browse files

Documentation: fpga: move fpga overview to driver-api 



Start of moving Documentation/fpga/*.txt to driver-api, including:
 - Add new directory driver-api/fpga
 - Add new file driver-api/fpga/index.rst
 - Add driver-api/fpga to driver-api/index.rst
 - Move Documentation/fpga/overview.txt to driver-api/fpga/intro.rst
 - Formatting and rewrites so that intro.rst will build cleanly
   and form a good introduction to the rest of the docs to be added.

Signed-off-by: default avatarAlan Tull <atull@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 917a4304

Documentation/driver-api/fpga/index.rst

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==============

FPGA Subsystem

==============



:Author: Alan Tull



.. toctree::

   :maxdepth: 2



   intro

Documentation/driver-api/fpga/intro.rst

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Introduction

============



The FPGA subsystem supports reprogramming FPGAs dynamically under

Linux.  Some of the core intentions of the FPGA subsystems are:



* The FPGA subsystem is vendor agnostic.



* The FPGA subsystem separates upper layers (userspace interfaces and

  enumeration) from lower layers that know how to program a specific

  FPGA.



* Code should not be shared between upper and lower layers.  This

  should go without saying.  If that seems necessary, there's probably

  framework functionality that that can be added that will benefit

  other users.  Write the linux-fpga mailing list and maintainers and

  seek out a solution that expands the framework for broad reuse.



* Generally, when adding code, think of the future.  Plan for re-use.



The framework in the kernel is divided into:



FPGA Manager

------------



If you are adding a new FPGA or a new method of programming a FPGA,

this is the subsystem for you.  Low level FPGA manager drivers contain

the knowledge of how to program a specific device.  This subsystem

includes the framework in fpga-mgr.c and the low level drivers that

are registered with it.



FPGA Bridge

-----------



FPGA Bridges prevent spurious signals from going out of a FPGA or a

region of a FPGA during programming.  They are disabled before

programming begins and re-enabled afterwards.  An FPGA bridge may be

actual hard hardware that gates a bus to a cpu or a soft ("freeze")

bridge in FPGA fabric that surrounds a partial reconfiguration region

of an FPGA.  This subsystem includes fpga-bridge.c and the low level

drivers that are registered with it.



FPGA Region

-----------



If you are adding a new interface to the FPGA framework, add it on top

of a FPGA region to allow the most reuse of your interface.



The FPGA Region framework (fpga-region.c) associates managers and

bridges as reconfigurable regions.  A region may refer to the whole

FPGA in full reconfiguration or to a partial reconfiguration region.



The Device Tree FPGA Region support (of-fpga-region.c) handles

reprogramming FPGAs when device tree overlays are applied.

Documentation/driver-api/index.rst

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@@ -49,6 +49,7 @@ available subsections can be seen below. 
   dmaengine/index

   dmaengine/index

   slimbus

   slimbus

   soundwire/index

   soundwire/index

   fpga/index





.. only::  subproject and html

.. only::  subproject and html

Documentation/fpga/overview.txt

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Linux kernel FPGA support



Alan Tull 2017



The main point of this project has been to separate the out the upper layers

that know when to reprogram a FPGA from the lower layers that know how to

reprogram a specific FPGA device.  The intention is to make this manufacturer

agnostic, understanding that of course the FPGA images are very device specific

themselves.



The framework in the kernel includes:

* low level FPGA manager drivers that know how to program a specific device

* the fpga-mgr framework they are registered with

* low level FPGA bridge drivers for hard/soft bridges which are intended to

  be disable during FPGA programming

* the fpga-bridge framework they are registered with

* the fpga-region framework which associates and controls managers and bridges

  as reconfigurable regions

* the of-fpga-region support for reprogramming FPGAs when device tree overlays

  are applied.



I would encourage you the user to add code that creates FPGA regions rather

that trying to control managers and bridges separately.