Kernel driver exynos_tmu¶
ARM Samsung Exynos4, Exynos5 series of SoC
Datasheet: Not publicly available
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:
Two point trimming:
Tc = (T - 25) * (TI2 - TI1) / (85 - 25) + TI1
One point trimming:
Tc = T + TI1 - 25
Tc = T + 50
- Temperature code, T: Temperature,
- Trimming info for 25 degree Celsius (stored at TRIMINFO register) Temperature code measured at 25 degree Celsius which is unchanged
- 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, cpufreq_cooling.c) ^ | | 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)
- 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.
- TMU driver:
- This component initialises the TMU controller and sets different thresholds. It invokes core thermal implementation with the call exynos_report_trigger.
- 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.