[U-Boot] [PATCH v11 13/16] regmap: Add overview documentation

[Mario Six]

Add some overview documentation that explains the purpose and some of
the features and limitations of the regmap interface.

Reviewed-by: Bin Meng <bmeng.cn at gmail.com>
Signed-off-by: Mario Six <mario.six at gdsys.cc>

---
v10 -> v11:
No changes

v9 -> v10:
No changes

v8 -> v9:
* Amended for inclusion of endianness setting via DT

v7 -> v8:
New in v8
---
 include/regmap.h | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/include/regmap.h b/include/regmap.h
index 98860c2732..b2b733fda6 100644
--- a/include/regmap.h
+++ b/include/regmap.h
@@ -7,6 +7,33 @@
 #ifndef __REGMAP_H
 #define __REGMAP_H

+/**
+ * DOC: Overview
+ *
+ * Regmaps are an abstraction mechanism that allows device drivers to access
+ * register maps irrespective of the underlying bus architecture. This entails
+ * that for devices that support multiple busses (e.g. I2C and SPI for a GPIO
+ * expander chip) only one driver has to be written. This driver will
+ * instantiate a regmap with a backend depending on the bus the device is
+ * attached to, and use the regmap API to access the register map through that
+ * bus transparently.
+ *
+ * Read and write functions are supplied, which can read/write data of
+ * arbitrary length from/to the regmap.
+ *
+ * The endianness of regmap accesses is selectable for each map through device
+ * tree settings via the boolean "little-endian", "big-endian", and
+ * "native-endian" properties.
+ *
+ * Furthermore, the register map described by a regmap can be split into
+ * multiple disjoint areas called ranges. In this way, register maps with
+ * "holes", i.e. areas of addressable memory that are not part of the register
+ * map, can be accessed in a concise manner.
+ *
+ * Currently, only a bare "mem" backend for regmaps is supported, which
+ * accesses the register map as regular IO-mapped memory.
+ */
+
 /**
  * enum regmap_size_t - Access sizes for regmap reads and writes
  *
--
2.18.1