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: Alan Tull <atull@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alan Tull 2018-05-16 18:50:02 -05:00 committed by Greg Kroah-Hartman
parent 917a4304fe
commit 66c472cdb6
4 changed files with 65 additions and 23 deletions

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==============
FPGA Subsystem
==============
:Author: Alan Tull
.. toctree::
:maxdepth: 2
intro

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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.

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dmaengine/index
slimbus
soundwire/index
fpga/index
.. only:: subproject and html

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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.