iMX8M Mini/Nano definition and usage of Kernel/Linux DTS file with more than one MIPI Display

[cedric_starke]

Hi at all people out there,

I actually need some help of defining the kernel/linux DTS file and use it together with the uboot videoargs.

In use is the 5.4.47-2.2.0 uboot and kernel/linux from the YOCTO manifest imx-5.4.47-2.2.0.xml.

In uboot i already can use 5 different MIPI displays and the HDMI adapter from nxp. To configure the display type I use the video_link environment variable. This works fine for me and can easily extended and configured. To get this work my uboot DTS looks like this:

#include <dt-bindings/usb/pd.h>
#include "imx8mm.dtsi"

/ {
	model = "My own board";
	compatible = "fsl,imx8mm-evk", "fsl,imx8mm";
	
	.
	.
	.
	
	dsi_host: dsi-host {
		compatible = "samsung,sec-mipi-dsi";
		status = "okay";
	};	

	01_panel {
		compatible = "mydisplay,01_display";
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_mipi_dsi_en>;
		reset-gpio = <&gpio1 8 GPIO_ACTIVE_LOW>;
		dsi-lanes = <4>;
		video-mode = <2>;	/* 0: burst mode
					 * 1: non-burst mode with sync event
					 * 2: non-burst mode with sync pulse
					 */
		panel-width-mm = <67>;
		panel-height-mm = <121>;
		status = "okay";

		port {
			01_from_dsim: endpoint {
				remote-endpoint = <&dsim_to_01>;
			};
		};
	};

	02_panel {
		compatible = "mydisplay,02_display";
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_mipi_dsi_en>;
		reset-gpio = <&gpio1 8 GPIO_ACTIVE_LOW>;
		dsi-lanes = <4>;
		video-mode = <2>;	/* 0: burst mode
					 * 1: non-burst mode with sync event
					 * 2: non-burst mode with sync pulse
					 */
		panel-width-mm = <67>;
		panel-height-mm = <121>;
		status = "okay";

		port {
			02_from_dsim: endpoint {
				remote-endpoint = <&dsim_to_02>;
			};
		};
	};

	.
	.
	.
};

.
.
.

&mipi_dsi {
	status = "okay";

	port@1 {
		dsim_to_adv7535: endpoint {
			remote-endpoint = <&adv7535_from_dsim>;
		};
	};

	port@2 {
		dsim_to_01: endpoint {
			remote-endpoint = <&01_from_dsim>;
		};
	};

	port@3 {
		dsim_to_02: endpoint {
			remote-endpoint = <&02_from_dsim>;
		};
	};
	
	.
	.
	.
};

Now I want to use the same displays in kernel/linux, of course. I first tried the same DTS structure like above from uboot DTS file. Also I used the following configuration of the kernel/linux DTS:

#include "imx8mm.dtsi"

/ {
	model = "My own board";
	compatible = "fsl,imx8mm-flunder", "fsl,imx8mm";
	reserved-memory {
		#address-cells = <2>;
		#size-cells = <2>;
		ranges;

		rpmsg_reserved: rpmsg@0xb8000000 {
			no-map;
			reg = <0 0xb8000000 0 0x400000>;
		};
	};
	
	.
	.
	.
};

.
.
.

&mipi_dsi {
  status = "okay";

	port@1 {
		dsim_to_adv7535: endpoint {
			remote-endpoint = <&adv7535_from_dsim>;
		};
	};

	panel@0 {
		compatible = "mydisplay,01_display";
		pinctrl-names = "default";
		reg = <0>;
		pinctrl-0 = <&pinctrl_mipi_dsi_en>;
		reset-gpio = <&gpio1 8 GPIO_ACTIVE_LOW>;
		dsi-lanes = <4>;
		video-mode = <2>;	/* 0: burst mode
						* 1: non-burst mode with sync event
						* 2: non-burst mode with sync pulse
						*/
		panel-width-mm = <62>;
		panel-height-mm = <110>;
		status = "okay";
	};

	panel@1 {
		compatible = "mydisplay,02_display";
		pinctrl-names = "default";
		reg = <0>;
		pinctrl-0 = <&pinctrl_mipi_dsi_en>;
		reset-gpio = <&gpio1 8 GPIO_ACTIVE_LOW>;
		dsi-lanes = <4>;
		video-mode = <2>;	/* 0: burst mode
						* 1: non-burst mode with sync event
						* 2: non-burst mode with sync pulse
						*/
		panel-width-mm = <62>;
		panel-height-mm = <110>;
		status = "okay";
	};
};

.
.
.

The second variant ends in the usage of the panel 0, while kernel boot. But in both variants I was not able to tell the kernel/linux, from the uboot side, which display I want to use.

As boot- or videoargs from uboot side I tested many variants without any success.

A short example list you can see here:

video=imx-drm:720x1280@60
primary_display=imx-drm
video=DSI-1:dev=01,720x1280@60
video=mxcfb0:dev=ldb,01_panel,if=RGB24
video=mxcfb0:dev=mipi_dsi,01_panel,if=RGB24
video=DSI-1:dev=01_panel
video=mxcfb0:dev=mipi_dsi,720x1280M@60,if=RGB24
video=mxcfb0:dev=ldb,720x1280M@60,if=RGB24
video=DSI-1:720x1280@60

In my opinion the first configuration, like I use in uboot, is the correct one, but I end in the questions:

How is the correct configuration of the kernel/linux DTS file for more then one MIPI DSI Display?

How can I tell the Kernel while booting which display it has it use?

For any help I would very thankful, because this issue already cost me to much time to solve.

Best regards

Cedric

[igorpadykov]

Hi Cedric

for custom mipi-dsi lcd one can use rm67191 driver example:

https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mm-evk-r...

https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/gpu/drm/panel/panel-raydium-rm6719...

make necessary modifications in struct cmd_set_entry manufacturer_cmd_set[],

lcd initialization can be found in lcd datasheet, timings in struct drm_display_mode default_mode

Best regards
igor

[cedric_starke]

Hi @igorpadykov 

Thanks for your quick answer. But the driver isn't my problem.

I have five new drivers implemented, based on the rm67191, which work well alone. But when I want to use all drivers together and tell the kernel from uboot which display I want to use I didn't find any solution till yet. Of course I do never use more then one display while runtime, but in one device is panel_01 and in the other one panel_02. For both I want tu use the same image and configure the display type only by a uboot environment variable like I can use in uboot with video_link.

Understandable?

Best regards

Cedric

[igorpadykov · Accepted solution]

one can consider dts overlay :

https://www.kernel.org/doc/html/latest/devicetree/overlay-notes.html

also as this is general linux question not i.mx specific, may be recommended to

post it on kernel mail list:

http://vger.kernel.org/vger-lists.html

Best regards
igor