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118 lines
3.7 KiB
Text
118 lines
3.7 KiB
Text
The U-Boot Driver Model Project
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===============================
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Hwmon device subsystem analysis
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===============================
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Tomas Hlavacek <tmshlvck@gmail.com>
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2012-03-02
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I) Overview
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-----------
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U-Boot currently implements one API for HW monitoring devices. The
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interface is defined in include/dtt.h and comprises of functions:
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void dtt_init(void);
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int dtt_init_one(int);
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int dtt_read(int sensor, int reg);
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int dtt_write(int sensor, int reg, int val);
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int dtt_get_temp(int sensor);
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The functions are implemented by a proper device driver in drivers/hwmon
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directory and the driver to be compiled in is selected in a Makefile.
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Drivers are mutually exclusive.
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Drivers depends on I2O code and naturally on board specific data. There are
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few ad-hoc constants put in dtt.h file and driver headers and code. This
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has to be consolidated into board specific data or driver headers if those
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constants makes sense globally.
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II) Approach
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------------
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1) New API
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----------
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In the UDM each hwmon driver would register itself by a function
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int hwmon_device_register(struct instance *i,
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struct hwmon_device_ops *o);
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The structure being defined as follows:
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struct hwmon_device_ops {
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int (*read)(struct instance *i, int sensor, int reg);
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int (*write)(struct instance *i, int sensor, int reg,
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int val);
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int (*get_temp)(struct instance *i, int sensor);
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};
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2) Conversion thougths
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----------------------
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U-Boot hwmon drivers exports virtually the same functions (with exceptions)
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and we are considering low number of drivers and code anyway. The interface
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is already similar and unified by the interface defined in dtt.h.
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Current initialization functions dtt_init() and dtt_init_one() will be
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converted into probe() and hwmon_device_register(), so the funcionality will
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be kept in more proper places. Besides implementing core registration and
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initialization we need to do code cleanup, especially separate
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driver-specific and HW specific constants.
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3) Special consideration due to early initialization
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----------------------------------------------------
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The dtt_init() function call is used during early initialization in
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board/gdsys/405ex/io64.c for starting up fans. The dtt code is perfectly
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usable in the early stage because it uses only local variables and no heap
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memory is required at this level. However the underlying code of I2C has to
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keep the same properties with regard to possibility of running in early
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initialization stage.
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III) Analysis of in-tree drivers
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--------------------------------
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1) drivers/hwmon/lm81.c
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-----------------------
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The driver is standard dtt. Simple conversion is possible.
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2) drivers/hwmon/ds1722.c
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-------------------------
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The driver is not standard dtt, but interface is similar to dtt.
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The interface has to be changed in order to comply to above mentioned
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specification.
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3) drivers/hwmon/ds1775.c
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-------------------------
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The driver is standard dtt. Simple conversion is possible.
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4) drivers/hwmon/lm73.c
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-----------------------
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The driver is standard dtt. Simple conversion is possible.
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5) drivers/hwmon/lm63.c
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-----------------------
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The driver is standard dtt. Simple conversion is possible.
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6) drivers/hwmon/adt7460.c
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--------------------------
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The driver is standard dtt. Simple conversion is possible.
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7) drivers/hwmon/lm75.c
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-----------------------
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The driver is standard dtt. Simple conversion is possible.
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8) drivers/hwmon/ds1621.c
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-------------------------
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The driver is standard dtt. Simple conversion is possible.
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9) drivers/hwmon/adm1021.c
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--------------------------
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The driver is standard dtt. Simple conversion is possible.
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