1 # 2 # (C) Copyright 2014 Samsung Electronics 3 # Lukasz Majewski <l.majewski (at] samsung.com> 4 # 5 # SPDX-License-Identifier: GPL-2.0+ 6 # 7 8 Introduction 9 ------------ 10 11 This document describes the second version of the u-boot's PMIC (Power 12 Management IC) framework. As a reference boards please consider Samsungs' Trats 13 and Trats2. 14 15 Background 16 ---------- 17 18 Boards supported by u-boot are getting increasingly complex. Developers and 19 designers strive to cut down power consumption. Hence several different types of 20 devices are now available on the board - namely power managers (PMIC), fuel 21 gauges (FG), micro USB interface controllers (MUIC), batteries, multi-function 22 devices (MFD). 23 24 Explanation of key design decisions 25 ----------------------------------- 26 27 One package can integrate PMIC and MUIC with different addresses on the I2C bus. 28 The same device - e.g. MAX8997 uses two different I2C busses and addresses. 29 30 Power devices use not only I2C for communication, but SPI as well. Additionally 31 different ICs use different endianess. For this reason struct pmic holds 32 information about I2C/SPI transmission, which is used with generic 33 pmic_req_write() function. 34 35 The "flat" hierarchy for power devices works well when each device performs only 36 one operation - e.g. PMIC enables LDO. 37 38 The problem emerges when we have a device (battery) which conceptually shall be 39 the master and uses methods exported by other devices. We need to control MUIC 40 to start charging the battery, use PMIC to reduce board's overall power 41 consumption (by disabling not needed LDOs, BUCKs) and get current state of 42 energy on the battery from FG. 43 Up till now u-boot doesn't support device model, so a simple one had to be 44 added. 45 46 The directory hierarchy has following structure: 47 ./include/power/<device_name>_<device_function>.h 48 e.g. ./include/power/max8997_pmic.h 49 50 ./drivers/power/pmic/power_{core files}.c 51 e.g. ./drivers/power/pmic/power_core.c 52 53 ./drivers/power/pmic/<device_function>/<device_function>_<device_name>.c 54 e.g. ./drivers/power/pmic/pmic_max8997.c 55 e.g. ./drivers/power/battery/trats/bat_trats.c 56 e.g. ./drivers/power/fuel_gauge/fg_max17042.c 57 58 The framework classifies devices by their function - separate directories should 59 be maintained for different classes of devices. 60 61 Current design 62 -------------- 63 64 Everything is a power device described by struct pmic. Even battery is 65 considered as a valid power device. This helps for better management of those 66 devices. 67 68 - Block diagram of the hierarchy: 69 ----------------- 70 --------| BAT |------------ 71 | | | | 72 | ----------------- | 73 | | | 74 \|/ \|/ \|/ 75 ----------- ----------------- --------- 76 |FG | |MUIC | |CHRG | 77 | | | | | | 78 ----------- ----------------- --------- 79 80 81 1. When hierarchy is not needed (no complex battery charge): 82 83 Definition of the struct pmic is only required with proper name and parameters 84 for communication. This is enough to use the "pmic" command in the u-boot 85 prompt to change values of device's register (enable/disable LDO, BUCK). 86 87 The PG, MUIC and CHRG above are regarded to be in the same level in the 88 hierarchy. 89 90 2. Complex battery charging. 91 92 To charge a battery, information from several "abstract" power devices is 93 needed (defined at ./include/power/pmic.h): 94 - FG device (struct power_fg): 95 -- *fg_battery_check - check if battery is not above its limits 96 -- *fg_battery_update - update the pmic framework with current 97 battery state(voltage and current capacity) 98 99 - Charger device (struct power_chrq): 100 -- *chrg_type - type/capacity of the charger (including information 101 about USB cable disconnection) 102 -- *chrg_bat_present - detection if battery to be charged is 103 present 104 -- *chrg_state - status of the charger - if it is enabled or 105 disabled 106 107 - Battery device (struct power_battery): 108 -- *battery_init - assign proper callbacks to be used by top 109 hierarchy battery device 110 -- *battery_charge - called from "pmic" command, responsible 111 for performing the charging 112 113 Now two batteries are supported; trats and trats2 [*]. Those differ in the way 114 how they handle the exact charging. Trats uses polling (MAX8997) and trats2 115 relies on the PMIC/MUIC HW completely (MAX77693). 116 117 __Example for trats (this can be very different for other board):__ 118 -- *fg_battery_check -> FG device (fg_max17042.c) 119 -- *fg_battery_update -> FG device (fg_max17042.c) 120 -- *chrg_type -> MUIC device (muic_max8997.c) 121 -- *chrg_bat_present -> PMIC device (pmic_max8997.c) 122 -- *chrg_state -> PMIC device (pmic_max8997.c) 123 -- *battery_init -> BAT device (bat_trats.c) 124 -- *battery_charge -> BAT device (bat_trats.c) 125 126 Also the struct pmic holds method (*low_power_mode) for reducing board's 127 power consumption when one calls "pmic BAT_TRATS bat charge" command. 128 129 How to add a new power device 130 ----------------------------- 131 132 1. Simple device should be added with creation of file 133 <pmic_function>_<pmic_name>.c, <pmic_name>_<pmic_function>.h according to the 134 proposed and described above scheme. 135 136 Then "pmic" command supports reading/writing/dump of device's internal 137 registers. 138 139 2. Charging battery with hierarchy 140 Define devices as listed at 1. 141 142 Define battery file (bat_<board>.c). Please also note that one might need a 143 corresponding battery model description for FG. 144 145 For points 1 and 2 use a generic function power_init_board() to initialise the 146 power framework on your board. 147 148 For reference, please look into the trats/trats2 boards. 149 150 TO DO list (for PMICv3) - up till v2014.04 151 ------------------------------------------ 152 153 1. Description of the devices related to power via device tree is not available. 154 This is the main problem when a developer tries to build a multi-boot u-boot 155 binary. The best would be to parse the DTS from Linux kernel. 156 157 2. To support many instances of the same IC, like two MAX8997, one needs to 158 copy the corresponding pmic_max8997.c file with changed name to "MAX8997_PMICX", 159 where X is the device number. This problem will be addressed when extended 160 pmic_core.c will support storing available devices in a list. 161 162 3. Definition of batteries [*] (for trats/trats2) should be excluded from the 163 code responsible for charging them and since it in fact describes the charging 164 profile it should be put to a separate file. 165 166 4. Adjust the framework to work with the device model. 167
