Imx6 debugging LVDS screen technical notes

Open the corresponding device tree file

	
mxcfb1: [email protected]0 {
    
		compatible = "fsl,mxc_sdc_fb";
		disp_dev = "ldb";// Display device 
		interface_pix_fmt = "RGB24";// Format 
		default_bpp = <32>;
		int_clk = <0>;
		late_init = <0>;
		status = "okay";
};

&ldb {
    
	status = "okay";
	dual-mode = <1>;

	lvds-[email protected]0 {
    
		reg = <0>;
		fsl,data-mapping = "spwg";
		fsl,data-width = <24>;
		status = "okay";
		primary;
		display-timings {
    
			native-mode = <&timing0>;
			timing0: hsd100pxn1 {
    
				clock-frequency = <164000000>;
				hactive = <1280>;
				vactive = <800>;
				hback-porch = <70>;
				hfront-porch = <70>;
				hsync-len = <20>;
				vback-porch = <12>;
				vfront-porch = <16>;	
				vsync-len = <4>;
			
			};
		};
	};
};

Single channel is : primary
Dual channel :split-mode ( notes : Two device nodes are required :[email protected] and [email protected])
after split-mode After the model ,lvds Of each channel signal pixelclock Become the original general , The horizontal effective length becomes half of the original , therefore , We can draw datasheet Medium pixelclock2=DI Terminal pixelclock,hacktive length 2=DI Terminal hacktive length . Simply put, it's the clock 2,hacktive2.

hback-porch/hfront-porch Equal parameter , Sometimes specifications are given directly , Sometimes you need to configure it yourself , But they all satisfy the following formula :
VP（ Total height ）= VBP(Vback-porch)+VFP(Vfront-porch)+VSPW(vsync-len)+VDP（ Effective resolution ）
VP（ Total width ）= HBP(Hback-porch)+HFP(Hfront-porch)+HSPW(Hsync-len)+HDP（ Effective resolution ）
VSPW（min）< VSPW<VBP
HSPW（min）<HSPW<HBP

Open the specification file on the screen

Find out , Configure the corresponding parameters of the device tree according to the content

Problem analysis

1、 If the ldb node , When starting, the screen doesn't even have a backlight .
analysis : Just look at the schematic diagram if necessary , Whether the enable pin is set to control the screen , If there is , It needs to be set to high level in the drive .

2、 If the back is bright , It doesn't show .
analysis : May be hback-porch And other configuration parameters are not configured correctly .

3. If a picture can appear , But the picture is constantly shaking .
analysis : It's the clock , You can try to turn the clock up , See if there is any improvement .