5 Replies Latest reply on Jan 26, 2015 9:15 PM by Cedric.P

    Where is the device tree?


      While digging into the linux kernel I found several different data structures that appear to be created from the device tree.From the kernel source code and documentation,I think I have a high-level understanding of the idea of the device tree but I don't know where it is located (in firmware somewhere?). I searched the source code from yocto and wasn't able to find anything that looked like it to me. Does anyone know where I can find its definition and hopefully make changes?

        • 1. Re: Where is the device tree?

          Hi Dferyance,


          This is a very interesting question, I am new in this topic but I let me see if I can help you with your research, are you searching a .dtb or a .dts  file or a graphical view of the device tree?

          Related to device modification for example, you can view and modify the GPIO and PWM if you go to root@clanton:/sys/kernel/debug

          • 2. Re: Where is the device tree?

            I am looking for the dts file and a way of editing it. This is partly for curiosity but I also am interested for changing the way the CS pins are defined for SPI. Right now there are only two CS pins available which isn't much as one is already used by the SPI flash. There is a data structure in the Linux SPI driver that can map CS indexes to GPIO pins but it looks like it isn't populated. I am not sure where it comes from but it might be from the device tree. If I could change this, it would be easy to add Linux driver support for multiple SPI devices.

            • 3. Re: Where is the device tree?

              Hi Dferyance,


              I noticed that you have looked into the SPI speed on the Galileo in detail in a few posts. I would be interested to hear if you have managed to find a way to increase the speed. I am having issues with SPI speed in Arduino.




              • 4. Re: Where is the device tree?

                Regarding the device tree, I’d recommend you to check for it in the Yocto source. You can also try looking for this in the Yocto Forum, there might be some information on this in there.

                • 5. Re: Where is the device tree?

                  The device tree may come from the SFI tables which are usually provided by the BIOS on a computer. I don't know where to find it for the Galileo or the Edison though.

                  See this post: Edison FW SFI Tables