Use LVDS 10.1 Display on BananaPiPro Mainline

[Pepsifan]

Hi,

 

I've not much experience on linux, so I want to ask some questions I don't find enough or helpful information getting an overview how things work. Not really an concrete question.

 

My goal is to run an 10.1 LVDS Display with silent boot and CAN-Bus on an BananaPi Pro. The SoC Allwinner A20 seems to support this, the board has an connector for this kind of Display. After flashing an SD with the image for BananaPi Pro and successfully booting from it, I read the Armbian Documentation. But I don't getting an overview, how the boot and configuration of u-Boot works. 

 

After "googleing" I understand the boot-process like this: 

Armbian seems to use U-Boot as Bootloader. The Bootloader is started by the Firmware of the SoC. The Bootloader takes the zImage (Linux Kernel Image) AND an DeviceTreeBlob (.dtb) file to get hardware info and Kernel together and starts the System up - device tree (DT) principle for ARM devices. 

For this there must be an "zImage" AND an "*.dtb" file in /boot. But direcly in this directory I just find the first one, the image. I've downloaded the SD-Image exactly for the BananaPiPro, so I wonder, where U-Boot gets the information about the DeviceTree, if not in /boot. 

Another question is: Where is the U-Boot configuration file?  The boot.cmd? (I don't find an file like "uboot.cfg", which would be self-explaining).

 

In the Armbian documentation (Hardware_Allwinner) is mentioned a "CONFIG_VIDEO_LCD_MODE" for "Kconfig", but no info, what this means. I found out, this seems to be an generic config-file, everywhere in Linux context. If I google this config string, I find the sunxi doc.( http://linux-sunxi.org/LCD ) But there too, I don't understand, where to set. It is in the Kernelmodul, must it be get compiled new, or is it just an configfile? If so, where to find?

 

Is armbianEnv.txt the U-Boot config file - or just for DeviceTree? When it gets read and it takes effect?

 

Somebody will know what the documentations mean and has an overview. It would be very nice to write some explainations, not just me would be grateful. Or just tell me, what you think I need to get of knowledge.

 

 

Greetings

Pepsifan

 

 

 

 

[Igor]

On 9/12/2017 at 2:40 PM, Pepsifan said:

For this there must be an "zImage" AND an "*.dtb" file in /boot. But direcly in this directory I just find the first one, the image. I've downloaded the SD-Image exactly for the BananaPiPro, so I wonder, where U-Boot gets the information about the DeviceTree, if not in /boot. 

 

DT is only for mainline kernels and it resists in /boot/dtb/ directory. There are usually more than one DT since the kernel is made for more boards at the same time. Which one has to be loaded is defined in u-boot. You can override this in armbianEnv.txt which is loaded by u-boot start script (boot.scr). If you by mistake started with the legacy kernel, there is no DT but Allwinner way of defining things.

 

On 9/12/2017 at 2:40 PM, Pepsifan said:

Somebody will know what the documentations mean and has an overview.

 

We can only cover onboard hardware. Even that proves to be an extremely hard job. 3rd party hardware is on your own, but perhaps you could find people, who have done this, here.

[zador.blood.stained]

On 12.09.2017 at 3:40 PM, Pepsifan said:

so I wonder, where U-Boot gets the information about the DeviceTree, if not in /boot. 

Board specific configuration (like DT name) is defined at compile time. For the mainline kernel LCD configuration needs to be changed at compile time too by changing the u-boot configuration.

 

On 12.09.2017 at 3:40 PM, Pepsifan said:

Another question is: Where is the U-Boot configuration file?  The boot.cmd? (I don't find an file like "uboot.cfg", which would be self-explaining).

http://git.denx.de/?p=u-boot.git;a=tree;f=configs;h=233bf28f904122bb1772d1d1995d8e7fde10dfae;hb=HEAD

 

Kconfig system generates the full configuration prior to the compilation.