IMX6q Wandboard LCD Device Tree Configuration for Display

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IMX6q Wandboard LCD Device Tree Configuration for Display

Postby asirastarfish » Wed Oct 19, 2016 5:52 pm

Hi everyone,

I created a linux image following the robert nelson instructions Located Here. It works for the most part, however I'm having difficulties configuring the display. I want the system to display on the parallel LCD output. It is doing this however all the current configurations are telling the system to use the HDMI. So I can't make any changes to the display timings to correct the data output. The output is accessible in /dev/fb0.

Currently the uEnv.txt instructs the system to use HDMI like so: cmdline=video=HDMI-A-1:1024x768@60e
Additionally the device tree explicity disables the ldb. Despite all of this however the default build still displays on the parallel LCD. However the clock rate and timings are incorrect.

imx6q-wandboard-revb1.dts is being used to build the dtb blob. imx6qdl-wandboard-revb1.dtsi, imx6qdl.dtsi and imx6q.dtsi get included in the build source. Those last two contain definitions for the ldb, which explicity disable it. After decompiling the .dtb for the ubuntu 14.04 wandboard image which did provide the functionality I needed I tried modifying the new device tree files to match the configuration of the wandboard stock image. The trouble is whenever I try to enable the LDB, the /dev/fb0 doesn't appear anymore no matter what I try.

Between all of the different files not specifying anything I'm not sure why it's displaying on the parallel LCD to begin with. When I modified the stock wandboard dtb I was able to add timing info the the LVDS channel and make the LCD run perfectly.

lvds-channel@0 {
reg = <0x0>;
status = "okay";
fsl,data-mapping = "spwg";
fsl,data-width = <0x18>;
primary;
crtc = "ipu1-di1";
display-timings {
native-mode = <0x14>;
hj070na {
clock-frequency = <0x30a32c0>;
hactive = <0x400>;
vactive = <0x258>;
hback-porch = <0x5a>;
hfront-porch = <0x78>;
vback-porch = <0x1>;
vfront-porch = <0x1>;
hsync-len = <0x64>;
vsync-len = <0x21>;
linux,phandle = <0x14>;
phandle = <0x14>;
pixelclk-active = "active high";
};
};
};
However attempting to do this with the new files makes the display completely fail. I'm uncertain on how to continue at this point. The main questions I have are:

1. How can I go about correctly editing the device tree to display on the LCD and allow me to configure it properly? How do I go about properly defining a new frame buffer?
2. How is the system displaying on the parallel LCD interface despite being explicitly disabled?

Thanks!
asirastarfish
 
Posts: 3
Joined: Thu Aug 25, 2016 11:47 pm

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