| Tomas Hlavacek | 1e5e9de | 2012-08-08 01:42:25 +0000 | [diff] [blame] | 1 | The U-Boot Driver Model Project |
| 2 | =============================== |
| 3 | Hwmon device subsystem analysis |
| 4 | =============================== |
| 5 | |
| 6 | Tomas Hlavacek <tmshlvck@gmail.com> |
| 7 | 2012-03-02 |
| 8 | |
| 9 | I) Overview |
| 10 | ----------- |
| 11 | |
| 12 | U-Boot currently implements one API for HW monitoring devices. The |
| 13 | interface is defined in include/dtt.h and comprises of functions: |
| 14 | |
| 15 | void dtt_init(void); |
| 16 | int dtt_init_one(int); |
| 17 | int dtt_read(int sensor, int reg); |
| 18 | int dtt_write(int sensor, int reg, int val); |
| 19 | int dtt_get_temp(int sensor); |
| 20 | |
| 21 | The functions are implemented by a proper device driver in drivers/hwmon |
| 22 | directory and the driver to be compiled in is selected in a Makefile. |
| 23 | Drivers are mutually exclusive. |
| 24 | |
| 25 | Drivers depends on I2O code and naturally on board specific data. There are |
| 26 | few ad-hoc constants put in dtt.h file and driver headers and code. This |
| 27 | has to be consolidated into board specific data or driver headers if those |
| 28 | constants makes sense globally. |
| 29 | |
| 30 | |
| 31 | II) Approach |
| 32 | ------------ |
| 33 | |
| 34 | 1) New API |
| 35 | ---------- |
| 36 | In the UDM each hwmon driver would register itself by a function |
| 37 | |
| 38 | int hwmon_device_register(struct instance *i, |
| 39 | struct hwmon_device_ops *o); |
| 40 | |
| 41 | The structure being defined as follows: |
| 42 | |
| 43 | struct hwmon_device_ops { |
| 44 | int (*read)(struct instance *i, int sensor, int reg); |
| 45 | int (*write)(struct instance *i, int sensor, int reg, |
| 46 | int val); |
| 47 | int (*get_temp)(struct instance *i, int sensor); |
| 48 | }; |
| 49 | |
| 50 | |
| 51 | 2) Conversion thougths |
| 52 | ---------------------- |
| 53 | U-Boot hwmon drivers exports virtually the same functions (with exceptions) |
| 54 | and we are considering low number of drivers and code anyway. The interface |
| 55 | is already similar and unified by the interface defined in dtt.h. |
| 56 | Current initialization functions dtt_init() and dtt_init_one() will be |
| 57 | converted into probe() and hwmon_device_register(), so the funcionality will |
| 58 | be kept in more proper places. Besides implementing core registration and |
| 59 | initialization we need to do code cleanup, especially separate |
| 60 | driver-specific and HW specific constants. |
| 61 | |
| 62 | 3) Special consideration due to early initialization |
| 63 | ---------------------------------------------------- |
| 64 | The dtt_init() function call is used during early initialization in |
| 65 | board/gdsys/405ex/io64.c for starting up fans. The dtt code is perfectly |
| 66 | usable in the early stage because it uses only local variables and no heap |
| 67 | memory is required at this level. However the underlying code of I2C has to |
| 68 | keep the same properties with regard to possibility of running in early |
| 69 | initialization stage. |
| 70 | |
| 71 | III) Analysis of in-tree drivers |
| 72 | -------------------------------- |
| 73 | |
| 74 | 1) drivers/hwmon/lm81.c |
| 75 | ----------------------- |
| 76 | The driver is standard dtt. Simple conversion is possible. |
| 77 | |
| 78 | |
| 79 | 2) drivers/hwmon/ds1722.c |
| 80 | ------------------------- |
| 81 | The driver is not standard dtt, but interface is similar to dtt. |
| 82 | The interface has to be changed in order to comply to above mentioned |
| 83 | specification. |
| 84 | |
| 85 | |
| 86 | 3) drivers/hwmon/ds1775.c |
| 87 | ------------------------- |
| 88 | The driver is standard dtt. Simple conversion is possible. |
| 89 | |
| 90 | |
| 91 | 4) drivers/hwmon/lm73.c |
| 92 | ----------------------- |
| 93 | The driver is standard dtt. Simple conversion is possible. |
| 94 | |
| 95 | |
| 96 | 5) drivers/hwmon/lm63.c |
| 97 | ----------------------- |
| 98 | The driver is standard dtt. Simple conversion is possible. |
| 99 | |
| 100 | |
| 101 | 6) drivers/hwmon/adt7460.c |
| 102 | -------------------------- |
| 103 | The driver is standard dtt. Simple conversion is possible. |
| 104 | |
| 105 | |
| 106 | 7) drivers/hwmon/lm75.c |
| 107 | ----------------------- |
| 108 | The driver is standard dtt. Simple conversion is possible. |
| 109 | |
| 110 | |
| 111 | 8) drivers/hwmon/ds1621.c |
| 112 | ------------------------- |
| 113 | The driver is standard dtt. Simple conversion is possible. |
| 114 | |
| 115 | |
| 116 | 9) drivers/hwmon/adm1021.c |
| 117 | -------------------------- |
| 118 | The driver is standard dtt. Simple conversion is possible. |