thermal: introduce device tree parser

This patch introduces a device tree bindings for
describing the hardware thermal behavior and limits.
Also a parser to read and interpret the data and feed
it in the thermal framework is presented.

This patch introduces a thermal data parser for device
tree. The parsed data is used to build thermal zones
and thermal binding parameters. The output data
can then be used to deploy thermal policies.

This patch adds also documentation regarding this
API and how to define tree nodes to use
this infrastructure.

Note that, in order to be able to have control
on the sensor registration on the DT thermal zone,
it was required to allow changing the thermal zone
.get_temp callback. For this reason, this patch
also removes the 'const' modifier from the .ops
field of thermal zone devices.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>

1 files changed, 595 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/thermal/thermal.txt b/Documentation/devicetree/bindings/thermal/thermal.txt
new file mode 100644
index 000000000000..f5db6b72a36f
--- /dev/null
+++ b/Documentation/devicetree/bindings/thermal/thermal.txt
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+* Thermal Framework Device Tree descriptor
+
+This file describes a generic binding to provide a way of
+defining hardware thermal structure using device tree.
+A thermal structure includes thermal zones and their components,
+such as trip points, polling intervals, sensors and cooling devices
+binding descriptors.
+
+The target of device tree thermal descriptors is to describe only
+the hardware thermal aspects. The thermal device tree bindings are
+not about how the system must control or which algorithm or policy
+must be taken in place.
+
+There are five types of nodes involved to describe thermal bindings:
+- thermal sensors: devices which may be used to take temperature
+  measurements.
+- cooling devices: devices which may be used to dissipate heat.
+- trip points: describe key temperatures at which cooling is recommended. The
+  set of points should be chosen based on hardware limits.
+- cooling maps: used to describe links between trip points and cooling devices;
+- thermal zones: used to describe thermal data within the hardware;
+
+The following is a description of each of these node types.
+
+* Thermal sensor devices
+
+Thermal sensor devices are nodes providing temperature sensing capabilities on
+thermal zones. Typical devices are I2C ADC converters and bandgaps. These are
+nodes providing temperature data to thermal zones. Thermal sensor devices may
+control one or more internal sensors.
+
+Required property:
+- #thermal-sensor-cells: Used to provide sensor device specific information
+  Type: unsigned	 while referring to it. Typically 0 on thermal sensor
+  Size: one cell	 nodes with only one sensor, and at least 1 on nodes
+			 with several internal sensors, in order
+			 to identify uniquely the sensor instances within
+			 the IC. See thermal zone binding for more details
+			 on how consumers refer to sensor devices.
+
+* Cooling device nodes
+
+Cooling devices are nodes providing control on power dissipation. There
+are essentially two ways to provide control on power dissipation. First
+is by means of regulating device performance, which is known as passive
+cooling. A typical passive cooling is a CPU that has dynamic voltage and
+frequency scaling (DVFS), and uses lower frequencies as cooling states.
+Second is by means of activating devices in order to remove
+the dissipated heat, which is known as active cooling, e.g. regulating
+fan speeds. In both cases, cooling devices shall have a way to determine
+the state of cooling in which the device is.
+
+Any cooling device has a range of cooling states (i.e. different levels
+of heat dissipation). For example a fan's cooling states correspond to
+the different fan speeds possible. Cooling states are referred to by
+single unsigned integers, where larger numbers mean greater heat
+dissipation. The precise set of cooling states associated with a device
+(as referred to be the cooling-min-state and cooling-max-state
+properties) should be defined in a particular device's binding.
+For more examples of cooling devices, refer to the example sections below.
+
+Required properties:
+- cooling-min-state:	An integer indicating the smallest
+  Type: unsigned	cooling state accepted. Typically 0.
+  Size: one cell
+
+- cooling-max-state:	An integer indicating the largest
+  Type: unsigned	cooling state accepted.
+  Size: one cell
+
+- #cooling-cells:	Used to provide cooling device specific information
+  Type: unsigned	while referring to it. Must be at least 2, in order
+  Size: one cell      	to specify minimum and maximum cooling state used
+			in the reference. The first cell is the minimum
+			cooling state requested and the second cell is
+			the maximum cooling state requested in the reference.
+			See Cooling device maps section below for more details
+			on how consumers refer to cooling devices.
+
+* Trip points
+
+The trip node is a node to describe a point in the temperature domain
+in which the system takes an action. This node describes just the point,
+not the action.
+
+Required properties:
+- temperature:		An integer indicating the trip temperature level,
+  Type: signed		in millicelsius.
+  Size: one cell
+
+- hysteresis:		A low hysteresis value on temperature property (above).
+  Type: unsigned	This is a relative value, in millicelsius.
+  Size: one cell
+
+- type:			a string containing the trip type. Expected values are:
+	"active":	A trip point to enable active cooling
+	"passive":	A trip point to enable passive cooling
+	"hot":		A trip point to notify emergency
+	"critical":	Hardware not reliable.
+  Type: string
+
+* Cooling device maps
+
+The cooling device maps node is a node to describe how cooling devices
+get assigned to trip points of the zone. The cooling devices are expected
+to be loaded in the target system.
+
+Required properties:
+- cooling-device:	A phandle of a cooling device with its specifier,
+  Type: phandle +	referring to which cooling device is used in this
+    cooling specifier	binding. In the cooling specifier, the first cell
+			is the minimum cooling state and the second cell
+			is the maximum cooling state used in this map.
+- trip:			A phandle of a trip point node within the same thermal
+  Type: phandle of	zone.
+   trip point node
+
+Optional property:
+- contribution:		The cooling contribution to the thermal zone of the
+  Type: unsigned	referred cooling device at the referred trip point.
+  Size: one cell      	The contribution is a ratio of the sum
+			of all cooling contributions within a thermal zone.
+
+Note: Using the THERMAL_NO_LIMIT (-1UL) constant in the cooling-device phandle
+limit specifier means:
+(i)   - minimum state allowed for minimum cooling state used in the reference.
+(ii)  - maximum state allowed for maximum cooling state used in the reference.
+Refer to include/dt-bindings/thermal/thermal.h for definition of this constant.
+
+* Thermal zone nodes
+
+The thermal zone node is the node containing all the required info
+for describing a thermal zone, including its cooling device bindings. The
+thermal zone node must contain, apart from its own properties, one sub-node
+containing trip nodes and one sub-node containing all the zone cooling maps.
+
+Required properties:
+- polling-delay:	The maximum number of milliseconds to wait between polls
+  Type: unsigned	when checking this thermal zone.
+  Size: one cell
+
+- polling-delay-passive: The maximum number of milliseconds to wait
+  Type: unsigned	between polls when performing passive cooling.
+  Size: one cell
+
+- thermal-sensors:	A list of thermal sensor phandles and sensor specifier
+  Type: list of 	used while monitoring the thermal zone.
+  phandles + sensor
+  specifier
+
+- trips:		A sub-node which is a container of only trip point nodes
+  Type: sub-node	required to describe the thermal zone.
+
+- cooling-maps:		A sub-node which is a container of only cooling device
+  Type: sub-node	map nodes, used to describe the relation between trips
+			and cooling devices.
+
+Optional property:
+- coefficients:		An array of integers (one signed cell) containing
+  Type: array		coefficients to compose a linear relation between
+  Elem size: one cell	the sensors listed in the thermal-sensors property.
+  Elem type: signed	Coefficients defaults to 1, in case this property
+			is not specified. A simple linear polynomial is used:
+			Z = c0 * x0 + c1 + x1 + ... + c(n-1) * x(n-1) + cn.
+
+			The coefficients are ordered and they match with sensors
+			by means of sensor ID. Additional coefficients are
+			interpreted as constant offset.
+
+Note: The delay properties are bound to the maximum dT/dt (temperature
+derivative over time) in two situations for a thermal zone:
+(i)  - when passive cooling is activated (polling-delay-passive); and
+(ii) - when the zone just needs to be monitored (polling-delay) or
+when active cooling is activated.
+
+The maximum dT/dt is highly bound to hardware power consumption and dissipation
+capability. The delays should be chosen to account for said max dT/dt,
+such that a device does not cross several trip boundaries unexpectedly
+between polls. Choosing the right polling delays shall avoid having the
+device in temperature ranges that may damage the silicon structures and
+reduce silicon lifetime.
+
+* The thermal-zones node
+
+The "thermal-zones" node is a container for all thermal zone nodes. It shall
+contain only sub-nodes describing thermal zones as in the section
+"Thermal zone nodes". The "thermal-zones" node appears under "/".
+
+* Examples
+
+Below are several examples on how to use thermal data descriptors
+using device tree bindings:
+
+(a) - CPU thermal zone
+
+The CPU thermal zone example below describes how to setup one thermal zone
+using one single sensor as temperature source and many cooling devices and
+power dissipation control sources.
+
+#include <dt-bindings/thermal/thermal.h>
+
+cpus {
+	/*
+	 * Here is an example of describing a cooling device for a DVFS
+	 * capable CPU. The CPU node describes its four OPPs.
+	 * The cooling states possible are 0..3, and they are
+	 * used as OPP indexes. The minimum cooling state is 0, which means
+	 * all four OPPs can be available to the system. The maximum
+	 * cooling state is 3, which means only the lowest OPPs (198MHz@0.85V)
+	 * can be available in the system.
+	 */
+	cpu0: cpu@0 {
+		...
+		operating-points = <
+			/* kHz    uV */
+			970000  1200000
+			792000  1100000
+			396000  950000
+			198000  850000
+		>;
+		cooling-min-state = <0>;
+		cooling-max-state = <3>;
+		#cooling-cells = <2>; /* min followed by max */
+	};
+	...
+};
+
+&i2c1 {
+	...
+	/*
+	 * A simple fan controller which supports 10 speeds of operation
+	 * (represented as 0-9).
+	 */
+	fan0: fan@0x48 {
+		...
+		cooling-min-state = <0>;
+		cooling-max-state = <9>;
+		#cooling-cells = <2>; /* min followed by max */
+	};
+};
+
+ocp {
+	...
+	/*
+	 * A simple IC with a single bandgap temperature sensor.
+	 */
+	bandgap0: bandgap@0x0000ED00 {
+		...
+		#thermal-sensor-cells = <0>;
+	};
+};
+
+thermal-zones {
+	cpu-thermal: cpu-thermal {
+		polling-delay-passive = <250>; /* milliseconds */
+		polling-delay = <1000>; /* milliseconds */
+
+		thermal-sensors = <&bandgap0>;
+
+		trips {
+			cpu-alert0: cpu-alert {
+				temperature = <90000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "active";
+			};
+			cpu-alert1: cpu-alert {
+				temperature = <100000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "passive";
+			};
+			cpu-crit: cpu-crit {
+				temperature = <125000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "critical";
+			};
+		};
+
+		cooling-maps {
+			map0 {
+				trip = <&cpu-alert0>;
+				cooling-device = <&fan0 THERMAL_NO_LIMITS 4>;
+			};
+			map1 {
+				trip = <&cpu-alert1>;
+				cooling-device = <&fan0 5 THERMAL_NO_LIMITS>;
+			};
+			map2 {
+				trip = <&cpu-alert1>;
+				cooling-device =
+				    <&cpu0 THERMAL_NO_LIMITS THERMAL_NO_LIMITS>;
+			};
+		};
+	};
+};
+
+In the example above, the ADC sensor (bandgap0) at address 0x0000ED00 is
+used to monitor the zone 'cpu-thermal' using its sole sensor. A fan
+device (fan0) is controlled via I2C bus 1, at address 0x48, and has ten
+different cooling states 0-9. It is used to remove the heat out of
+the thermal zone 'cpu-thermal' using its cooling states
+from its minimum to 4, when it reaches trip point 'cpu-alert0'
+at 90C, as an example of active cooling. The same cooling device is used at
+'cpu-alert1', but from 5 to its maximum state. The cpu@0 device is also
+linked to the same thermal zone, 'cpu-thermal', as a passive cooling device,
+using all its cooling states at trip point 'cpu-alert1',
+which is a trip point at 100C. On the thermal zone 'cpu-thermal', at the
+temperature of 125C, represented by the trip point 'cpu-crit', the silicon
+is not reliable anymore.
+
+(b) - IC with several internal sensors
+
+The example below describes how to deploy several thermal zones based off a
+single sensor IC, assuming it has several internal sensors. This is a common
+case on SoC designs with several internal IPs that may need different thermal
+requirements, and thus may have their own sensor to monitor or detect internal
+hotspots in their silicon.
+
+#include <dt-bindings/thermal/thermal.h>
+
+ocp {
+	...
+	/*
+	 * A simple IC with several bandgap temperature sensors.
+	 */
+	bandgap0: bandgap@0x0000ED00 {
+		...
+		#thermal-sensor-cells = <1>;
+	};
+};
+
+thermal-zones {
+	cpu-thermal: cpu-thermal {
+		polling-delay-passive = <250>; /* milliseconds */
+		polling-delay = <1000>; /* milliseconds */
+
+				/* sensor       ID */
+		thermal-sensors = <&bandgap0     0>;
+
+		trips {
+			/* each zone within the SoC may have its own trips */
+			cpu-alert: cpu-alert {
+				temperature = <100000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "passive";
+			};
+			cpu-crit: cpu-crit {
+				temperature = <125000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "critical";
+			};
+		};
+
+		cooling-maps {
+			/* each zone within the SoC may have its own cooling */
+			...
+		};
+	};
+
+	gpu-thermal: gpu-thermal {
+		polling-delay-passive = <120>; /* milliseconds */
+		polling-delay = <1000>; /* milliseconds */
+
+				/* sensor       ID */
+		thermal-sensors = <&bandgap0     1>;
+
+		trips {
+			/* each zone within the SoC may have its own trips */
+			gpu-alert: gpu-alert {
+				temperature = <90000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "passive";
+			};
+			gpu-crit: gpu-crit {
+				temperature = <105000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "critical";
+			};
+		};
+
+		cooling-maps {
+			/* each zone within the SoC may have its own cooling */
+			...
+		};
+	};
+
+	dsp-thermal: dsp-thermal {
+		polling-delay-passive = <50>; /* milliseconds */
+		polling-delay = <1000>; /* milliseconds */
+
+				/* sensor       ID */
+		thermal-sensors = <&bandgap0     2>;
+
+		trips {
+			/* each zone within the SoC may have its own trips */
+			dsp-alert: gpu-alert {
+				temperature = <90000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "passive";
+			};
+			dsp-crit: gpu-crit {
+				temperature = <135000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "critical";
+			};
+		};
+
+		cooling-maps {
+			/* each zone within the SoC may have its own cooling */
+			...
+		};
+	};
+};
+
+In the example above, there is one bandgap IC which has the capability to
+monitor three sensors. The hardware has been designed so that sensors are
+placed on different places in the DIE to monitor different temperature
+hotspots: one for CPU thermal zone, one for GPU thermal zone and the
+other to monitor a DSP thermal zone.
+
+Thus, there is a need to assign each sensor provided by the bandgap IC
+to different thermal zones. This is achieved by means of using the
+#thermal-sensor-cells property and using the first cell of the sensor
+specifier as sensor ID. In the example, then, <bandgap 0> is used to
+monitor CPU thermal zone, <bandgap 1> is used to monitor GPU thermal
+zone and <bandgap 2> is used to monitor DSP thermal zone. Each zone
+may be uncorrelated, having its own dT/dt requirements, trips
+and cooling maps.
+
+
+(c) - Several sensors within one single thermal zone
+
+The example below illustrates how to use more than one sensor within
+one thermal zone.
+
+#include <dt-bindings/thermal/thermal.h>
+
+&i2c1 {
+	...
+	/*
+	 * A simple IC with a single temperature sensor.
+	 */
+	adc: sensor@0x49 {
+		...
+		#thermal-sensor-cells = <0>;
+	};
+};
+
+ocp {
+	...
+	/*
+	 * A simple IC with a single bandgap temperature sensor.
+	 */
+	bandgap0: bandgap@0x0000ED00 {
+		...
+		#thermal-sensor-cells = <0>;
+	};
+};
+
+thermal-zones {
+	cpu-thermal: cpu-thermal {
+		polling-delay-passive = <250>; /* milliseconds */
+		polling-delay = <1000>; /* milliseconds */
+
+		thermal-sensors = <&bandgap0>,	/* cpu */
+				  <&adc>;	/* pcb north */
+
+		/* hotspot = 100 * bandgap - 120 * adc + 484 */
+		coefficients = 		<100	-120	484>;
+
+		trips {
+			...
+		};
+
+		cooling-maps {
+			...
+		};
+	};
+};
+
+In some cases, there is a need to use more than one sensor to extrapolate
+a thermal hotspot in the silicon. The above example illustrates this situation.
+For instance, it may be the case that a sensor external to CPU IP may be placed
+close to CPU hotspot and together with internal CPU sensor, it is used
+to determine the hotspot. Assuming this is the case for the above example,
+the hypothetical extrapolation rule would be:
+		hotspot = 100 * bandgap - 120 * adc + 484
+
+In other context, the same idea can be used to add fixed offset. For instance,
+consider the hotspot extrapolation rule below:
+		hotspot = 1 * adc + 6000
+
+In the above equation, the hotspot is always 6C higher than what is read
+from the ADC sensor. The binding would be then:
+        thermal-sensors =  <&adc>;
+
+		/* hotspot = 1 * adc + 6000 */
+	coefficients = 		<1	6000>;
+
+(d) - Board thermal
+
+The board thermal example below illustrates how to setup one thermal zone
+with many sensors and many cooling devices.
+
+#include <dt-bindings/thermal/thermal.h>
+
+&i2c1 {
+	...
+	/*
+	 * An IC with several temperature sensor.
+	 */
+	adc-dummy: sensor@0x50 {
+		...
+		#thermal-sensor-cells = <1>; /* sensor internal ID */
+	};
+};
+
+thermal-zones {
+	batt-thermal {
+		polling-delay-passive = <500>; /* milliseconds */
+		polling-delay = <2500>; /* milliseconds */
+
+				/* sensor       ID */
+		thermal-sensors = <&adc-dummy     4>;
+
+		trips {
+			...
+		};
+
+		cooling-maps {
+			...
+		};
+	};
+
+	board-thermal: board-thermal {
+		polling-delay-passive = <1000>; /* milliseconds */
+		polling-delay = <2500>; /* milliseconds */
+
+				/* sensor       ID */
+		thermal-sensors = <&adc-dummy     0>, /* pcb top edge */
+				  <&adc-dummy     1>, /* lcd */
+				  <&adc-dymmy     2>; /* back cover */
+		/*
+		 * An array of coefficients describing the sensor
+		 * linear relation. E.g.:
+		 * z = c1*x1 + c2*x2 + c3*x3
+		 */
+		coefficients =		<1200	-345	890>;
+
+		trips {
+			/* Trips are based on resulting linear equation */
+			cpu-trip: cpu-trip {
+				temperature = <60000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "passive";
+			};
+			gpu-trip: gpu-trip {
+				temperature = <55000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "passive";
+			}
+			lcd-trip: lcp-trip {
+				temperature = <53000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "passive";
+			};
+			crit-trip: crit-trip {
+				temperature = <68000>; /* millicelsius */
+				hysteresis = <2000>; /* millicelsius */
+				type = "critical";
+			};
+		};
+
+		cooling-maps {
+			map0 {
+				trip = <&cpu-trip>;
+				cooling-device = <&cpu0 0 2>;
+				contribution = <55>;
+			};
+			map1 {
+				trip = <&gpu-trip>;
+				cooling-device = <&gpu0 0 2>;
+				contribution = <20>;
+			};
+			map2 {
+				trip = <&lcd-trip>;
+				cooling-device = <&lcd0 5 10>;
+				contribution = <15>;
+			};
+		};
+	};
+};
+
+The above example is a mix of previous examples, a sensor IP with several internal
+sensors used to monitor different zones, one of them is composed by several sensors and
+with different cooling devices.