Difference between revisions of "How to modify the panel backlight"

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Applicable for STM32MP13x lines, STM32MP15x lines

First identify the backlight device linked to your panel, thanks to the sysfs: 

 ls /sys/class/backlight
5a000000.dsi.0

In the above example, there is a single entry named "5a000000.dsi.0", which is replaced by "*" in the below command.


To adjust the panel backlight, enter the following command: 

 echo 32 > /sys/class/backlight/*/brightness    # set the dsi panel backlight to the value 32

Note: Only values between 0 and max_brightness must be used.

To get the maximum panel backlight value, enter: 

 cat /sys/class/backlight/*/max_brightness
255

To get the actual panel backlight value, enter: 

 cat /sys/class/backlight/*/actual_brightness
32


Use one of the following commands to quickly test the panel backlight: 

 export bl=/sys/class/backlight/5a000000.dsi.0/brightness

 # switch on/off test
 (while true; do echo 0 > $bl; sleep 0.5; echo 255 > $bl; sleep 0.5; done)

 # slow 32-step tests
 (i=0; while true; do i=$(((i+32)%256)); echo $i > $bl; sleep 0.5; done)

 # fast 1-step test
 (i=0; while true; do i=$(((i+1)%256)); echo $i > $bl; done)
Info white.png Information
Be sure the panel is running (power on) before modifying its backlight. 



<noinclude>{{ApplicableFor
|MPUs list=STM32MP13x, STM32MP15x
|MPUs checklist=STM32MP13x,STM32MP15x
}}</noinclude>

First identify the backlight device linked to your panel, thanks to the sysfs:
 {{Board$}} ls /sys/class/backlight
 5a000000.dsi.0

In the above example, there is a single entry named "5a000000.dsi.0", which is '''replaced by "*"''' in the below command.

To adjust the panel backlight, enter the following command:
 {{Board$}} echo '''32''' > /sys/class/backlight/*/'''brightness'''    # set the dsi panel backlight to the value '''32'''
Note: Only values between 0 and '''max_brightness''' must be used.

To get the maximum panel backlight value, enter:
 {{Board$}} cat /sys/class/backlight/*/'''max_brightness'''
 255

To get the actual panel backlight value, enter:
 {{Board$}} cat /sys/class/backlight/*/'''actual_brightness'''
 32

Use one of the following commands to quickly test the panel backlight:
 {{Board$}} export bl=/sys/class/backlight/5a000000.dsi.0/brightness

 {{Board$}} # switch on/off test
 {{Board$}} (while true; do echo 0 > $bl; sleep 0.5; echo 255 > $bl; sleep 0.5; done)

 {{Board$}} # slow 32-step tests
 {{Board$}} (i=0; while true; do i=$(((i+32)%256)); echo $i > $bl; sleep 0.5; done)

 {{Board$}} # fast 1-step test
 {{Board$}} (i=0; while true; do i=$(((i+1)%256)); echo $i > $bl; done)

{{Info | Be sure the panel is running (power on) before modifying its backlight.}}
<noinclude>

{{PublicationRequestId | 10715 | 2019-02-18 | AnneJ}}
[[Category:How to run use cases]]
[[Category:DRM KMS]]</noinclude>
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<noinclude>{{ApplicableFor
  +
|MPUs list=STM32MP13x, STM32MP15x
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|MPUs checklist=STM32MP13x,STM32MP15x
  +
}}</noinclude>
  +
 
First identify the backlight device linked to your panel, thanks to the sysfs:
  
First identify the backlight device linked to your panel, thanks to the sysfs:
 
  {{Board$}} ls /sys/class/backlight
  
  {{Board$}} ls /sys/class/backlight
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  {{Board$}} (i=0; while true; do i=$(((i+1)%256)); echo $i > $bl; done)
  
  {{Board$}} (i=0; while true; do i=$(((i+1)%256)); echo $i > $bl; done)
   
  +
{{Info | Be sure the panel is running (power on) before modifying its backlight.}}
   
 
<noinclude>
  
<noinclude>
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