Changes between Initial Version and Version 1 of linux/backlight


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Timestamp:
10/22/2017 05:28:45 AM (2 years ago)
Author:
trac
Comment:

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  • linux/backlight

    v1 v1  
     1{{{#!html
     2          <div id="wikipage" class="trac-content"><p>
     3</p><div class="wiki-toc">
     4<ol>
     5  <li>
     6    <a href="#LinuxBacklightclassdigitaldisplaybacklights">Linux Backlight class digital display backlights</a>
     7  </li>
     8  <li>
     9    <a href="#OtherReferences">Other References</a>
     10  </li>
     11</ol>
     12</div><p>
     13</p>
     14<p>
     15<span class="wikianchor" id="backlight_class"></span>
     16</p>
     17<h1 id="LinuxBacklightclassdigitaldisplaybacklights">Linux Backlight class digital display backlights</h1>
     18<p>
     19A digital display which has a backlight may have a Linux backlight driver which provides a sysfs API. Typically these are implemented via PWM signals allowing a variable brightness or a GPIO signal allowing a simple on/off.
     20</p>
     21<p>
     22Mapping A backlight driver to a PWM, GPIO, or other controller is done in the board support file or in the case of more modern kernels such as Ventana in the device-tree. See the backlight node in the <a class="ext-link" href="http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/imx6qdl-gw54xx.dtsi#n31"><span class="icon">​</span>gw54xx device-tree</a> for example.
     23</p>
     24<p>
     25To list available backlight controllers:
     26</p>
     27<pre class="wiki">ls /sys/class/backlight
     28</pre><p>
     29To see current/available brightness values:
     30</p>
     31<pre class="wiki">cat /sys/class/backlight/*/brightness # current brightness
     32cat /sys/class/backlight/*/max_brightness # max brightness
     33</pre><p>
     34To set brightness (to a value equal or less than max_brightness)
     35</p>
     36<pre class="wiki">echo 0 &gt; /sys/class/backlight/*/brightness # turn off backlight
     37</pre><p>
     38References:
     39</p>
     40<ul><li><a class="ext-link" href="http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.txt"><span class="icon">​</span>GPIO backlight</a>
     41</li><li><a class="ext-link" href="http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt"><span class="icon">​</span>PWM backlight</a>
     42</li><li><a class="ext-link" href="http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/stable/sysfs-class-backlight"><span class="icon">​</span>sysfs-class-backlight</a>
     43</li></ul><h1 id="OtherReferences">Other References</h1>
     44<p>
     45Here are some other useful references from our wiki:
     46</p>
     47<ul><li><a class="wiki" href="/wiki/gpio">General Purpose I/O (GPIO)</a>
     48</li><li><a class="wiki" href="/wiki/linux/pwm">Pulse-Width-Modulation (PWM)</a>
     49</li><li><a class="wiki" href="/wiki/OpenWrt/gpio">GPIO in OpenWrt</a>
     50</li><li><a class="wiki" href="/wiki/ventana/DigitalIO">Ventana product family Digital I/O</a>
     51</li></ul
     52}}}