title: configfs do not mount device-tree/overlays
body: <p>I'm working on a Cyclone V SOC FPGA from Altera with a double Cortex-A9 processor. The embedded system (linux 4.15.7) is created with Buildroot-2018.02. U-boot is used to load the system i-e FPGA.rbf file, device tree blob and zImage and everything works fine.</p>
  
  <p>I want now to integrate the RBF file to my linux and program the FPGA from Linux. I found several methods and the one I understand is the most common is to use CONFIGFS with a device-tree overlay.</p>
  
  <p>So I changed my device tree to integrate the overlay, the u-boot boot script to disable FPGA load and also the following options in the linux ".config" file with <code>make linux-xconfig</code> :</p>
  
  <pre><code>+CONFIG_OF_OVERLAY=y
  +CONFIG_ALTERA_STAPL=y
  +CONFIG_CONFIGFS_FS=y
  +CONFIG_SAMPLES=y
  +CONFIG_SAMPLE_CONFIGFS=m
  </code></pre>
  
  <p>These options are the state were I am now after several try.</p>
  
  <p>After a make and a reboot, once the kernel is loaded, I enter the following command in the console :</p>
  
  <pre><code>mkdir /config
  mount -t configfs none /config
  </code></pre>
  
  <p>At this state, I'm expecting to see some device tree files in the /config folder but there wasn't any, only one rdma_cm folder :</p>
  
  <pre><code># ls /config
  rdma_cm
  </code></pre>
  
  <p>I continued my reading on this topic and found that I must enable the CONFIG_OF_CONFIGFS option in my linux kernel.</p>
  
  <p>PROBLEM: This option is not available in my linux kernel. Also, file <code>drivers/of/configfs.c</code> is no here too. I've searched in vain to find how to enable device tree overlay for my kernel version.</p>
  
  <p>How can I configure my kernel to make device-tree available in configfs ?</p>