Documentation/thermal/exynos_thermal

   1 Kernel driver exynos_tmu
   2 =================
   3
   4 Supported chips:
   5 * ARM SAMSUNG EXYNOS4, EXYNOS5 series of SoC
   6   Datasheet: Not publicly available
   7
   8 Authors: Donggeun Kim <dg77.kim@samsung.com>
   9 Authors: Amit Daniel <amit.daniel@samsung.com>
  10
  11 TMU controller Description:
  12 ---------------------------
  13
  14 This driver allows to read temperature inside SAMSUNG EXYNOS4/5 series of SoC.
  15
  16 The chip only exposes the measured 8-bit temperature code value
  17 through a register.
  18 Temperature can be taken from the temperature code.
  19 There are three equations converting from temperature to temperature code.
  20
  21 The three equations are:
  22   1. Two point trimming
  23         Tc = (T - 25) * (TI2 - TI1) / (85 - 25) + TI1
  24
  25   2. One point trimming
  26         Tc = T + TI1 - 25
  27
  28   3. No trimming
  29         Tc = T + 50
  30
  31   Tc: Temperature code, T: Temperature,
  32   TI1: Trimming info for 25 degree Celsius (stored at TRIMINFO register)
  33        Temperature code measured at 25 degree Celsius which is unchanged
  34   TI2: Trimming info for 85 degree Celsius (stored at TRIMINFO register)
  35        Temperature code measured at 85 degree Celsius which is unchanged
  36
  37 TMU(Thermal Management Unit) in EXYNOS4/5 generates interrupt
  38 when temperature exceeds pre-defined levels.
  39 The maximum number of configurable threshold is five.
  40 The threshold levels are defined as follows:
  41   Level_0: current temperature > trigger_level_0 + threshold
  42   Level_1: current temperature > trigger_level_1 + threshold
  43   Level_2: current temperature > trigger_level_2 + threshold
  44   Level_3: current temperature > trigger_level_3 + threshold
  45
  46   The threshold and each trigger_level are set
  47   through the corresponding registers.
  48
  49 When an interrupt occurs, this driver notify kernel thermal framework
  50 with the function exynos_report_trigger.
  51 Although an interrupt condition for level_0 can be set,
  52 it can be used to synchronize the cooling action.
  53
  54 TMU driver description:
  55 -----------------------
  56
  57 The exynos thermal driver is structured as,
  58
  59                                         Kernel Core thermal framework
  60                                 (thermal_core.c, step_wise.c, cpu_cooling.c)
  61                                                                 ^
  62                                                                 |
  63                                                                 |
  64 TMU configuration data -------> TMU Driver  <------> Exynos Core thermal wrapper
  65 (exynos_tmu_data.c)           (exynos_tmu.c)       (exynos_thermal_common.c)
  66 (exynos_tmu_data.h)           (exynos_tmu.h)       (exynos_thermal_common.h)
  67
  68 a) TMU configuration data: This consist of TMU register offsets/bitfields
  69                 described through structure exynos_tmu_registers. Also several
  70                 other platform data (struct exynos_tmu_platform_data) members
  71                 are used to configure the TMU.
  72 b) TMU driver: This component initialises the TMU controller and sets different
  73                 thresholds. It invokes core thermal implementation with the call
  74                 exynos_report_trigger.
  75 c) Exynos Core thermal wrapper: This provides 3 wrapper function to use the
  76                 Kernel core thermal framework. They are exynos_unregister_thermal,
  77                 exynos_register_thermal and exynos_report_trigger.