dt: bindings: Add documentation for pwm-fan

Device tree properties used in pwm-fan is Documented in
Documentation/devicetree/bindings to understand how are
the properties used in driver.

Bug 200563459

Change-Id: I08bd23fc6c19410924c7007c2cc2a6542c0f5499
Signed-off-by: Sandipan patra <spatra@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2239766
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Tested-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/thermal/tegra-pwm-fan.txt b/Documentation/devicetree/bindings/thermal/tegra-pwm-fan.txt
new file mode 100644
index 000000000..30a9935c4
--- /dev/null
+++ b/Documentation/devicetree/bindings/thermal/tegra-pwm-fan.txt
@@ -0,0 +1,51 @@
+Bindings for a fan connected to the PWM lines
+
+Properties details:
+- compatible            : "pwm-fan"
+- pwms                  : the PWM that is used to control the PWM fan
+
+- shared_data
+  - active_steps        : Entries for references in active_rpm[], active_pwm[], active_rru[], active_rrd[]
+  - active_rru          : This value is kept on added to cur_pwm till it reaches at
+                          next active step from the table. This is repeated until cur_pwm
+                          value reaches target_pwm
+  - active_rrd          : This value is kept on subtracted from cur_pwm till it reaches at
+                          previous active step from the table. This is repeated until cur_pwm
+                          value reaches target_pwm
+  - state_cap_lookup    : Index to refer in active_pwm[]
+  - pwm_period          : To derive duty cycle
+  - pwm_id              : Assigned PWM controller id to tegra fan
+                          Same as mentioned id in pwms. In pwms, the id starts from 1
+                          pwm_id in pfsd, the id starts from 0
+  - step_time           : Time taken for each step during rru/rrd
+  - state_cap           : Capping state value out of available active_steps
+  - active_pwm_max      : Max pwm value (256)
+  - pwm_gpio            : GPIO pin used for pwm
+
+Example:
+
+        pwm_fan_shared_data: pfsd {
+                status = "okay";
+                num_resources = <0>;
+                active_steps = <10>;
+                active_rpm = <0 1000 2000 3000 4000 5000 6000 7000 10000 11000>;
+                active_rru = <40 2 1 1 1 1 1 1 1 1>;
+                active_rrd = <40 2 1 1 1 1 1 1 1 1>;
+                state_cap_lookup = <2 2 2 2 3 3 3 4 4 4>;
+                pwm_period = <45334>;
+                pwm_id = <3>;
+                step_time = <100>; /* mesecs */
+                state_cap = <7>;
+                active_pwm_max = <256>;
+                pwm_gpio = <&tegra_aon_gpio TEGRA_AON_GPIO(V, 6) GPIO_ACTIVE_LOW>; /* TEGRA_MAIN_GPIO_PV6 */
+        };
+        pwm-fan {
+                status = "okay";
+                compatible = "pwm-fan";
+                #pwm-cells = <1>;
+                pwms = <&tegra_pwm4 0 45334>;
+                shared_data = <&pwm_fan_shared_data>;
+                active_pwm = <0 80 120 160 255 255 255 255 255 255>;
+        };
+};
+