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========================
Kernel driver exynos_tmu
========================
Supported chips:
* ARM SAMSUNG EXYNOS4, EXYNOS5 series of SoC
Datasheet: Not publicly available
Authors: Donggeun Kim <dg77.kim@samsung.com>
Authors: Amit Daniel <amit.daniel@samsung.com>
TMU controller Description:
---------------------------
This driver allows to read temperature inside SAMSUNG EXYNOS4/5 series of SoC.
The chip only exposes the measured 8-bit temperature code value
through a register.
Temperature can be taken from the temperature code.
There are three equations converting from temperature to temperature code.
The three equations are:
1. Two point trimming::
Tc = (T - 25) * (TI2 - TI1) / (85 - 25) + TI1
2. One point trimming::
Tc = T + TI1 - 25
3. No trimming::
Tc = T + 50
Tc:
Temperature code, T: Temperature,
TI1:
Trimming info for 25 degree Celsius (stored at TRIMINFO register)
Temperature code measured at 25 degree Celsius which is unchanged
TI2:
Trimming info for 85 degree Celsius (stored at TRIMINFO register)
Temperature code measured at 85 degree Celsius which is unchanged
TMU(Thermal Management Unit) in EXYNOS4/5 generates interrupt
when temperature exceeds pre-defined levels.
The maximum number of configurable threshold is five.
The threshold levels are defined as follows::
Level_0: current temperature > trigger_level_0 + threshold
Level_1: current temperature > trigger_level_1 + threshold
Level_2: current temperature > trigger_level_2 + threshold
Level_3: current temperature > trigger_level_3 + threshold
The threshold and each trigger_level are set
through the corresponding registers.
When an interrupt occurs, this driver notify kernel thermal framework
with the function exynos_report_trigger.
Although an interrupt condition for level_0 can be set,
it can be used to synchronize the cooling action.
TMU driver description:
-----------------------
The exynos thermal driver is structured as::
Kernel Core thermal framework
(thermal_core.c, step_wise.c, cpu_cooling.c)
^
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TMU configuration data -----> TMU Driver <----> Exynos Core thermal wrapper
(exynos_tmu_data.c) (exynos_tmu.c) (exynos_thermal_common.c)
(exynos_tmu_data.h) (exynos_tmu.h) (exynos_thermal_common.h)
a) TMU configuration data:
This consist of TMU register offsets/bitfields
described through structure exynos_tmu_registers. Also several
other platform data (struct exynos_tmu_platform_data) members
are used to configure the TMU.
b) TMU driver:
This component initialises the TMU controller and sets different
thresholds. It invokes core thermal implementation with the call
exynos_report_trigger.
c) Exynos Core thermal wrapper:
This provides 3 wrapper function to use the
Kernel core thermal framework. They are exynos_unregister_thermal,
exynos_register_thermal and exynos_report_trigger.
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