[RFC 7/7] capebus: Documentation; capebus-summary

[Pantelis Antoniou <panto@antoniou-consulting.com>]

Small summary of capebus.

Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
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+Overview of Linux kernel Capebus support
+========================================
+
+30-Oct-2012
+
+What is Capebus?
+----------------
+Capebus is an abstract concept. There's no such thing as a vanilla physical
+capebus, what is there is a concept and a method on how various capebus
+based implementations can be made.
+
+Capebus is created to address the problem of many SoCs that can provide a
+multitude of hardware interfaces but in order to keep costs down the main
+boards only support a limited number of them. The rest are typically brought
+out to pin connectors on to which other boards, named capes are connected and
+allow those peripherals to be used.
+
+These capes connect to the SoC interfaces but might also contain various other
+parts that may need some kind of driver to work.
+
+Since SoCs have limited pins and pin muxing options, not all capes can work
+together so some kind of resource tracking (at least for the pins in use) is
+required.
+
+Before capebus all of this took place in the board support file, and frankly
+for boards with too many capes it was becoming unmanageable.
+
+Capebus provides a virtual bus, which along with a board specific controller,
+cape drivers can be written using the standard Linux device model.
+
+What kind of systems/boards capebus supports?
+---------------------------------------------
+
+The core capebus infrastructure is not depended on any specific board.
+However capebus needs a board controller to provide services to the cape devices
+it controls. Services like addressing and resource reservation are provided
+by the board controller.
+
+Capebus at the moment only support TI's Beaglebone platform.
+
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1.7.12