dtb questions

Hello Alfred,

sdcard image has all device trees on the first partition. Normally you can use our default device trees. Over the time our experience shows that our customer use different combination of boot divice. E.g. it is possible to configure our bootloader to use device tree from NAND or USB and other images like linux kernel and rootfs from eMMC. Also we desided to add some more binaries to our sdcard tar ball. But they are same default images like in our bsp binaries folder.

If you want to use several device trees for armstonea9 you can e.g compile the binary manuelly and add (copy) it inside the sdcard image. This can be done by mounting the image as loopback device. You will find more information online. (e.g. on wikipedia) It should be a easiest and fastest way from my point of view.

For production it can be more better way to add the divice tree to the machine file fsimx6.conf in .../meta-fus/conf/machine directory and add the your device tree to the kernel. For this it need to:

• Extend the KERNEL_DEVICETREE enviroment with your device tree
• Add the patch to recipe ../meta-fus/recipse-kernel/linux/linux-fus.bb
• (Re)compile the kernel e.g. commado bitbake -c compile linux-fus -f
• Build your image again. E.g. bitbake fus-image-std
• Boot the board and go to the bootloader command line interface
• Change the environment bootfd to bootloader name, which should be used. E.g. cmd 'editenv bootfdt' allows to change the env. value.
• Optional use 'saveenv' command to write the new value to the persistent memory.

Hope this helps.

Your F&S Support Team

In the past, Linux did not use device trees. There used to be a board support file directly in the kernel that defined the devices that were available on that board. So there was one board support file for each board. This was very inflexible and required recompilation of the whole kernel if some device parameters like display resolution or timings changed.

In later kernels, the hardware description of a board was moved to the device tree. So now the device tree defines what hardware is available on the board and we only need a board-specific device tree file. The kernel can remain unchanged all the time. The switch to device trees on the fsimx6 architecture was done with the V3.0 release, hence the new major version number.

If you look at the device tree file armstonea9q.dts, you can see at the beginning some settings that you can change. Specifically the display configuration can be defined/modified there. You can define what displays (up to four) you actually use (CONFIG_ARMSTONEA9_MXCFB<n>) and what display parameters should be used for each of the displays (for example CONFIG_ARMSTONEA9_LVDS0_*). There are quite some long comments that should explain what you need to set. Then you have to recompile the device tree and install the new dtb file on the board.

However NXP was not very consistent when doing the switch to device trees. So the settings for LVDS and HDMI are completely done in the device tree, but the settings for the RGB-Interface are given in the device driver in file drivers/video/fbdev/mxc/mxc_lcdif.c. There are several settings provided (see the array lcdif_modedb at the beginning of the file) and you simply select one of the predefined settings by giving the Mode String, for example:

CONFIG_ARMSTONEA9_LCD_MODE_STR "LCD-ET070080"

Usually you can use one of the given timings. Only if your display has completely different settings, then you need to add a new entry to this table using a new Mode String, and then you have to recompile and reinstall the kernel, too. Of course you have to use this new Mode String in your device tree then.

Your F&S Support Team

There was no device tree back then. So you cannot extract the data from it. The resolution and timings were given as C-code in some struct in the board support file and is now hidden somehwere deep inside the large kernel image (which is gzipped, too, so no chance to find it). You need the source code from back then. Or try to create new timings from the data sheet of the display.

Your F&S Support Team

Hello,

I will have a look.

Could you write a mail with this request to support@fs-net.de?

Your F&S Support Team