doc: driver-model: Convert pmic-framework.txt to reST

Convert plain text documentation to reStructuredText format and add
it to Sphinx TOC tree. No essential content change.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

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+.. SPDX-License-Identifier: GPL-2.0+
+.. (C) Copyright 2014-2015 Samsung Electronics
+.. sectionauthor:: Przemyslaw Marczak <p.marczak@samsung.com>
+
+PMIC framework based on Driver Model
+====================================
+
+Introduction
+------------
+This is an introduction to driver-model multi uclass PMIC IC's support.
+At present it's based on two uclass types:
+
+UCLASS_PMIC:
+  basic uclass type for PMIC I/O, which provides common
+  read/write interface.
+UCLASS_REGULATOR:
+  additional uclass type for specific PMIC features, which are
+  Voltage/Current regulators.
+
+New files:
+
+UCLASS_PMIC:
+  - drivers/power/pmic/pmic-uclass.c
+  - include/power/pmic.h
+UCLASS_REGULATOR:
+  - drivers/power/regulator/regulator-uclass.c
+  - include/power/regulator.h
+
+Commands:
+- common/cmd_pmic.c
+- common/cmd_regulator.c
+
+How doees it work
+-----------------
+The Power Management Integrated Circuits (PMIC) are used in embedded systems
+to provide stable, precise and specific voltage power source with over-voltage
+and thermal protection circuits.
+
+The single PMIC can provide various functions by single or multiple interfaces,
+like in the example below::
+
+   -- SoC
+    |
+    |            ______________________________________
+    | BUS 0     |       Multi interface PMIC IC        |--> LDO out 1
+    | e.g.I2C0  |                                      |--> LDO out N
+    |-----------|---- PMIC device 0 (READ/WRITE ops)   |
+    | or SPI0   |    |_ REGULATOR device (ldo/... ops) |--> BUCK out 1
+    |           |    |_ CHARGER device (charger ops)   |--> BUCK out M
+    |           |    |_ MUIC device (microUSB con ops) |
+    | BUS 1     |    |_ ...                            |---> BATTERY
+    | e.g.I2C1  |                                      |
+    |-----------|---- PMIC device 1 (READ/WRITE ops)   |---> USB in 1
+    . or SPI1   |    |_ RTC device (rtc ops)           |---> USB in 2
+    .           |______________________________________|---> USB out
+    .
+
+Since U-Boot provides driver model features for I2C and SPI bus drivers,
+the PMIC devices should also support this. By the pmic and regulator API's,
+PMIC drivers can simply provide a common functions, for multi-interface and
+and multi-instance device support.
+
+Basic design assumptions:
+
+- Common I/O API:
+    UCLASS_PMIC. For the multi-function PMIC devices, this can be used as
+    parent I/O device for each IC's interface. Then, each children uses the
+    same dev for read/write.
+
+- Common regulator API:
+    UCLASS_REGULATOR. For driving the regulator attributes, auto setting
+    function or command line interface, based on kernel-style regulator device
+    tree constraints.
+
+For simple implementations, regulator drivers are not required, so the code can
+use pmic read/write directly.
+
+Pmic uclass
+-----------
+The basic information:
+
+* Uclass:   'UCLASS_PMIC'
+* Header:   'include/power/pmic.h'
+* Core:     'drivers/power/pmic/pmic-uclass.c' (config 'CONFIG_DM_PMIC')
+* Command:  'common/cmd_pmic.c' (config 'CONFIG_CMD_PMIC')
+* Example:  'drivers/power/pmic/max77686.c'
+
+For detailed API description, please refer to the header file.
+
+As an example of the pmic driver, please refer to the MAX77686 driver.
+
+Please pay attention for the driver's bind() method. Exactly the function call:
+'pmic_bind_children()', which is used to bind the regulators by using the array
+of regulator's node, compatible prefixes.
+
+The 'pmic; command also supports the new API. So the pmic command can be enabled
+by adding CONFIG_CMD_PMIC.
+The new pmic command allows to:
+- list pmic devices
+- choose the current device (like the mmc command)
+- read or write the pmic register
+- dump all pmic registers
+
+This command can use only UCLASS_PMIC devices, since this uclass is designed
+for pmic I/O operations only.
+
+For more information, please refer to the core file.
+
+Regulator uclass
+----------------
+The basic information:
+
+* Uclass: 'UCLASS_REGULATOR'
+
+* Header: 'include/power/regulator.h'
+
+* Core: 'drivers/power/regulator/regulator-uclass.c'
+  (config 'CONFIG_DM_REGULATOR')
+
+* Binding: 'doc/device-tree-bindings/regulator/regulator.txt'
+
+* Command: 'common/cmd_regulator.c' (config 'CONFIG_CMD_REGULATOR')
+
+* Example: 'drivers/power/regulator/max77686.c'
+  'drivers/power/pmic/max77686.c' (required I/O driver for the above)
+
+* Example: 'drivers/power/regulator/fixed.c'
+  (config 'CONFIG_DM_REGULATOR_FIXED')
+
+For detailed API description, please refer to the header file.
+
+For the example regulator driver, please refer to the MAX77686 regulator driver,
+but this driver can't operate without pmic's example driver, which provides an
+I/O interface for MAX77686 regulator.
+
+The second example is a fixed Voltage/Current regulator for a common use.
+
+The 'regulator' command also supports the new API. The command allow:
+- list regulator devices
+- choose the current device (like the mmc command)
+- do all regulator-specific operations
+
+For more information, please refer to the command file.