Aaron.lin at 08:53, 2 February 2017

2017-02-02T08:53:40Z

Aaron.lin: Created page with "'''1. How to set the pwm-backlight?''' pwm-backlight bindings Required properties:
- compatible: "pwm-backlight"
..."

2017-02-02T08:29:34Z

Created page with "'''1. How to set the pwm-backlight?''' pwm-backlight bindings Required properties: - compatible: "pwm-backlight" ..."

New page

'''1. How to set the pwm-backlight?'''

pwm-backlight bindings

Required properties:   - compatible: "pwm-backlight"   - pwms: OF device-tree PWM specification (see PWM binding[0])   - brightness-levels: Array of distinct brightness levels. Typically these       are in the range from 0 to 255, but any range starting at 0 will do.       The actual brightness level (PWM duty cycle) will be interpolated       from these values. 0 means a 0% duty cycle (darkest/off), while the       last value in the array represents a 100% duty cycle (brightest).   - default-brightness-level: the default brightness level (index into the       array defined by the "brightness-levels" property)   - power-supply: regulator for supply voltage

Optional properties:   - pwm-names: a list of names for the PWM devices specified in the                "pwms" property (see PWM binding[0])   - enable-gpios: contains a single GPIO specifier for the GPIO which enables                   and disables the backlight (see GPIO binding[1])

[0]: Documentation/devicetree/bindings/pwm/pwm.txt [1]: Documentation/devicetree/bindings/gpio/gpio.txt

Example:
<pre> backlight {
compatible = "pwm-backlight";
pwms = <&pwm 0 5000000>;

brightness-levels = <0 4 8 16 32 64 128 255>;
default-brightness-level = <6>;

power-supply = <&vdd_bl_reg>;
enable-gpios = <&gpio 58 0>;
};</pre>

In ELAA, you can set it in kernel_imx/arch/arm/boot/dts/imx6qdl-advantech.dtsi
<pre>...

bkl: backlight {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_lvds_bkl_1 &pinctrl_lvds_vcc_1>;
compatible = "pwm-backlight";
brightness-levels = <0 4 8 16 32 64 128 255>;
default-brightness-level = <7>;
status = "disabled";
};
...

</pre>



'''2. How to check the pwm-backlight path for Android'''

The pwm-backlight path is at /sys/class/backlight/backlight

We must make sure the pwm-backlight path is correct for Android.

For ROM 7421, the related file is device/fsl/rom_7421_a1/init.rc

For ROM 3420, the related file is device/fsl/rom_3420_a1/init.rc
<pre>....

# Default backlight device
setprop hw.backlight.dev "backlight"
# Chmod/chown FSL specific sys entry
chown system system /sys/class/backlight/backlight/brightness
chmod 0660 /sys/class/backlight/backlight/brightness
...</pre>

'''3. How to control pwm-backlight from Android setting'''

Go to Android (Settings--> Display--> Brightness level), to adjust the pwm-backlight bar, then check whether the backlight is changed as adjusting the control bar.

4. How to control pwm-backlight in command line
<pre>#cd /sys/class/backlight/backlight</pre>

'''a. check current brightness level'''
<pre># cat brightness</pre>

b. change the brightness level
<pre>#echo 3 > brightness</pre>

c. check the max brightness
<pre>#cat max_brightness
</pre>

''''''

@@ Line 36: / Line 36: @@
 </pre>
-<span style="font-size:large;"></span>
 <span style="font-size:large;">'''2. How to check the pwm-backlight path for Android'''</span>
@@ Line 57: / Line 57: @@
 '''<span style="font-size:large;">3. How to control pwm-backlight from Android setting</span>'''
@@ Line 64: / Line 66: @@
 . How to control pwm-backlight in command line
 <pre>#cd /sys/class/backlight/backlight</pre>
@@ Line 70: / Line 74: @@
 <pre># cat brightness</pre>
-b. change the brightness level
+'''b. change the brightness level'''
 <pre>#echo 3 > brightness</pre>
-c. check the max brightness
+'''c. check the max brightness'''
 <pre>#cat max_brightness
 </pre>
+'''e. turn on pwm backlight power'''
-'''<span style="font-size:large;"></span>'''
+<pre># echo 0 > bl_power</pre>

IoTGateway/BSP/Android/Gettingstarted/How to set LCD backlight using PWM - Revision history

Aaron.lin at 08:53, 2 February 2017

Aaron.lin: Created page with "'''1. How to set the pwm-backlight?''' pwm-backlight bindings Required properties: - compatible: "pwm-backlight" ..."

Aaron.lin: Created page with "'''1. How to set the pwm-backlight?''' pwm-backlight bindings Required properties:
- compatible: "pwm-backlight"
..."