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Subject[PATCH 1/2] dt-bindings: thermal: thermal_mmio: Add binding documentation
Date
Add thermal binding documentation for thermal MMIO driver.

Signed-off-by: Talel Shenhar <talel@amazon.com>
---
.../devicetree/bindings/thermal/thermal_mmio.txt | 173 +++++++++++++++++++++
1 file changed, 173 insertions(+)
create mode 100644 Documentation/devicetree/bindings/thermal/thermal_mmio.txt

diff --git a/Documentation/devicetree/bindings/thermal/thermal_mmio.txt b/Documentation/devicetree/bindings/thermal/thermal_mmio.txt
new file mode 100644
index 0000000..1f4d738
--- /dev/null
+++ b/Documentation/devicetree/bindings/thermal/thermal_mmio.txt
@@ -0,0 +1,173 @@
+Generic Thermal MMIO Driver
+
+The generic thermal driver enables easy connectivity between "simple"
+thermal HW devices to the thermal subsystem. "simple" - thermal HW that
+doesn't need any configuration (such as power reset or clock enable) by a
+driver and only exports the temperature via simple MMIO access, or,
+alternatively, all the configuration is done by other entity (e.g.
+bootloader).
+
+Any system that allows temperature reading via a single memory map read, be
+it register or shared memory, is a potential candidate to work with this
+driver.
+This driver allows manipulations on the read value in order to allow some
+flexibility for the various thermal HW, e.g. sensor-factor which will be
+multiplied by the read value.
+
+This driver is most suitable for cases such as the following:
+- The entire thermal HW setup (e.g. configure the thermal HW to work in
+ continuous mode) is done by another SW entity (e.g. bootloader) and all
+ that is left is to read the current temperature from a register
+- The thermal reading is done by an external CPU (e.g. micro-controller)
+ and that CPU is exporting the reading via a shared memory
+- The thermal HW setup and reading is done via CPLD, which exports the
+ current temperature to the system via a register
+- The thermal HW is working out-of-the-box and only reports temperature via
+ a single register access
+
+Some examples for cases that this driver is not suitable for:
+- Your HW need clock enabling to be done by thermal driver
+- Your HW need some registers configurations in order to start reporting
+ temperatures and it is not doable by other entities (e.g. bootloader)
+- Your HW allows reading of temperatures only between ADCs (or any other
+ timing constrains)
+- In case your HW was configured by a bootloader and it lose the
+ configuration as part of low-power-state and need to be reconfigured.
+ (bootloader configuration typically is not sustained across low power
+ states)
+- In case the reading from the MMIO require any type of locking
+
+So the only operation this driver will do is MMIO read for the temperature.
+In case you are using HW that require some configurations this driver is
+not suitable (you can decide to move all the configuration logic into your
+bootloader and only leave the temperature reading to this driver but this
+is up to you).
+
+An example of a system that uses this driver is the Amazon Nitro SoC in
+which there is the main CPU and micro-controller:
+(1) The micro-controller accesses an SBUS controller to read the thermal
+ sensor from an SBUS slave called Avago Technologies digital
+ Temperature/Voltage Sensor (ip16_SENS_thermvolt25_0)
+(2) Once the micro-controller gathers the temperature it relays it to the
+ main CPU via a Shared Integrated RAM which is MMIO accessible by the CPU
+(3) The thermal_mmio driver that runs on the main CPU will read the
+ temperature via an MMIO access to the Shared RAM
+
++------------------+ +----------------+
+| | (3) | |
+| Main CPU +----->+ Integrated RAM |
+| | | |
++------------------+ +---------^------+
+ |(2)
++-----------------+ +------------------+
+| | (1) | |
+| SBUS controller <-------+ micro-controller |
+| | | |
++--------+--------+ +------------------+
+ |
++--------v---------------------+
+| |
+| Avago Technologies digital |
+| Temperature/Voltage Sensor |
+| (ip16_SENS_thermvolt25_0) |
+| |
++------------------------------+
+
+Required properties:
+- compatible: "thermal-mmio".
+- reg: The physical base address and length of the sensor's registers.
+- #thermal-sensor-cells: Must be 1. See ./thermal.txt for a description.
+
+Optional properties:
+- sensor-width: Width (in bytes) of each consecutive sensor.
+ Supported: 1, 2, 4.
+ (Default = 4)
+- sensor-mask: Mask to be applied on the raw read value before any
+ calculation.
+ (Default = 0xFFFFFFFF)
+- sensor-factor: Scale value by which to multiple the masked read value
+ This is a signed 32 bit value.
+ (Default = 1)
+- sensor-bias: Bias value to be added to the scaled value.
+ This is a signed 32 bit value.
+ (Default = 0)
+- sensor-divider: Dividing value by which to divide the calculated value.
+ Diving will be Integer Division.
+ This is a unsigned 32 bit value.
+ (Default = 1)
+
+Conversion formula from HW MMIO read value to millidegrees (Celsius):
+T_millidegrees = (bias + (T_raw & mask)*factor)/divider
+
+Example 1, two thermal devices with one thermal sensor each, that uses only
+the required properties (uses default):
+
+ thermal_d1: thermal_d1 {
+ compatible = "thermal-mmio";
+ reg = <0x0 0x05002860 0x0 0x4>;
+ #thermal-sensor-cells = <0x1>;
+ };
+
+ thermal_d2: thermal_d2 {
+ compatible = "thermal-mmio";
+ reg = <0x0 0x05000730 0x0 0x4>;
+ #thermal-sensor-cells = <0x1>;
+ };
+
+ thermal-zones {
+ thermal_d1_z0 {
+ polling-delay-passive = <250>;
+ polling-delay = <1000>;
+ thermal-sensors = <&thermal_d1 0>;
+ trips {
+ thermal_d1_z0_crit {
+ temperature = <105000>;
+ hysteresis = <2000>;
+ type = "critical";
+ };
+ };
+
+ };
+
+ thermal_d2_z0 {
+ polling-delay-passive = <250>;
+ polling-delay = <1000>;
+ thermal-sensors = <&thermal_d2 0>;
+ trips {
+ thermal_d2_z0_crit {
+ temperature = <105000>;
+ hysteresis = <2000>;
+ type = "critical";
+ };
+ };
+ };
+ };
+
+Example 2, one thermal device with two sensors of 6 bits each each, that
+has a factor of -5, bias of 23 and dividing of 2:
+
+ thermal_d3: thermal_d3 {
+ compatible = "thermal-mmio";
+ reg = <0x0 0x05005700 0x0 0x2>;
+ #thermal-sensor-cells = <0x1>;
+ sensor-width = <1>;
+ sensor-mask = <0x3F>;
+ sensor-factor = <(-5)>;
+ sensor-bias = <23>;
+ sensor-divider = <2>;
+ };
+
+ thermal-zones {
+ thermal_d3 {
+ polling-delay-passive = <250>;
+ polling-delay = <1000>;
+ thermal-sensors = <&thermal_d3 0>;
+ trips {
+ thermal_d3_z0_crit {
+ temperature = <105000>;
+ hysteresis = <2000>;
+ type = "critical";
+ };
+ };
+ };
+ };
--
2.7.4
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