Disabling combined UART in JetPack 5.1.1 on Xavier NX

Autonomous Machines Jetson & Embedded Systems Jetson Xavier NX
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8

I made the changes below to the five files only. The net result was that the Xavier NX did not boot and did not even enter the UEFI shell. I have attached the log from the debug UART (which is clearly not fully disabled) debug_uart.log (10.4 KB).

JetPack 5.1.1 Device Tree Changes

p3668.conf.common

Changed:

	TBCDTB_FILE=tegra194-p3668-all-p3509-0000.dtb;
	CMDLINE_ADD="console=ttyTCU0,115200n8 console=tty0 fbcon=map:0 net.ifnames=0";
	target_board="t186ref";

to:

	TBCDTB_FILE=tegra194-p3668-all-p3509-0000.dtb;
	CMDLINE_ADD="console=tty0 fbcon=map:0 net.ifnames=0";
	target_board="t186ref";

tegra194-mb1-bct-misc-l4t.cfg

Changed:

        enable_combined_uart = 1;
        spe_uart_instance = 0x2;

to:

        enable_combined_uart = 0; # DRM: Disable combined UART
        spe_uart_instance = 0xFF; # DRM: Disable use of UART 2 for combined UART

tegra194-mb1-bct-misc-flash.cfg

Changed:

        enable_combined_uart = 1;
        spe_uart_instance = 0x2;

to:

        enable_combined_uart = 0; # DRM: Disable combined UART
        spe_uart_instance = 0xFF; # DRM: Disable use of UART 2 for combined UART

tegra194-a02-bpmp-p3668-a00.dtb

Changed:

		serial {
				port = <0x3>;
				has_input;
				
				combined-uart {
					enabled;
				}
		};

to:

		serial {
				port = <0xFF>; /* DRM: disable debugging to serial port */
				has_input;
				
				combined-uart {
				     disabled; /* DRM: was enabled */
				};
		};

tegra194-p3668-all-p3509-0000.dtb

Changed:

	combined-uart {
		compatible = "nvidia,tegra194-tcu\0nvidia,tegra186-combined-uart";
		reg = <0x00 0x3c10000 0x00 0x04 0x00 0xc168000 0x00 0x04 0x00 0x3c00000 0x00 0x1000>;
		interrupts = <0x00 0x78 0x04>;
		mboxes = <0x1c 0x01 0x00 0x1d 0x01 0x80000001>;
		mbox-names = "rx\0tx";
		skip-frame-info;
		status = "okay";
		console-port;
		combined-uart;
	};

to:

	combined-uart {
		compatible = "nvidia,tegra194-tcu\0nvidia,tegra186-combined-uart";
		reg = <0x00 0x3c10000 0x00 0x04 0x00 0xc168000 0x00 0x04 0x00 0x3c00000 0x00 0x1000>;
		interrupts = <0x00 0x78 0x04>;
		mboxes = <0x1c 0x01 0x00 0x1d 0x01 0x80000001>;
		mbox-names = "rx\0tx";
		skip-frame-info;
		status = "disabled"; /* DRM: was "okay" */
		console-port;
		combined-uart;
	};
9

Please help to provide the full flash log for further check.
And try to not modify tegra194-a02-bpmp-p3668-a00.dtb.

10

Here is the flash log: flash.log (581.3 KB). I will try building again without the modification to tegra194-a02-bpmp-p3668-a00.dtb.

11

Same problem. It doesn’t boot or enter the UEFI shell. Here is the output on the UART: debug_uart.log (22.6 KB)

12

Could you try removing serial { this node in tegra194-a02-bpmp-p3668-a00.dtb and do not modify both tegra194-mb1-bct-misc-l4t.cfg and tegra194-mb1-bct-misc-flash.cfg?

13

I made the changes below to the three files only. The net result was that the Xavier NX does boot successfully but the UART is clearly still being used as a debug UART during boot. I have attached the log from the debug UART
debug_port.log (12.1 KB). Also note that /dev/ttyTCU0 still exists so the combined UART is still being created.

JetPack 5.1.1 Device Tree Changes

p3668.conf.common

Changed:

	TBCDTB_FILE=tegra194-p3668-all-p3509-0000.dtb;
	CMDLINE_ADD="console=ttyTCU0,115200n8 console=tty0 fbcon=map:0 net.ifnames=0";
	target_board="t186ref";

to:

	TBCDTB_FILE=tegra194-p3668-all-p3509-0000.dtb;
	CMDLINE_ADD="console=tty0 fbcon=map:0 net.ifnames=0";
	target_board="t186ref";

tegra194-a02-bpmp-p3668-a00.dtb

Removed:

		serial {
				port = <0x3>;
				has_input;
				
				combined-uart {
					enabled;
				}
		};

tegra194-p3668-all-p3509-0000.dtb

Changed:

	combined-uart {
		compatible = "nvidia,tegra194-tcu\0nvidia,tegra186-combined-uart";
		reg = <0x00 0x3c10000 0x00 0x04 0x00 0xc168000 0x00 0x04 0x00 0x3c00000 0x00 0x1000>;
		interrupts = <0x00 0x78 0x04>;
		mboxes = <0x1c 0x01 0x00 0x1d 0x01 0x80000001>;
		mbox-names = "rx\0tx";
		skip-frame-info;
		status = "okay";
		console-port;
		combined-uart;
	};

to:

	combined-uart {
		compatible = "nvidia,tegra194-tcu\0nvidia,tegra186-combined-uart";
		reg = <0x00 0x3c10000 0x00 0x04 0x00 0xc168000 0x00 0x04 0x00 0x3c00000 0x00 0x1000>;
		interrupts = <0x00 0x78 0x04>;
		mboxes = <0x1c 0x01 0x00 0x1d 0x01 0x80000001>;
		mbox-names = "rx\0tx";
		skip-frame-info;
		status = "disabled"; /* DRM: was "okay" */
		console-port;
		combined-uart;
	};
14

Could you try to remove /dev/ttyTCU0 in this dtb?

It seems you’ve disabled all logs from kernel.
Does it meet your requirement?

15

I changed the tegra194-p3668-all-p3509-0000.dtb modification above to remove the combined-uart node altogether, as I understood you to suggest. The Xavier NX boots but the /dev/ttyTCU0 device still exists.

Re. my requirements, I am trying to eliminate the debug logs completely so that uartc is free for me to use. I do not wish to redirect the debug log to another serial port as I am using the other serial ports as well.

16

You could disable the status of combined-uart { in kernel dtb to remove this node.

It should be tegra194-p3668-0001-p3509-0000.dtb, please modify this file instead of tegra194-p3668-all-p3509-0000.dtb for your case.

It should be no serial logs output after kernel started and meet your requirement.

17

I tried your suggestion and it doesn’t work either. The /dev/ttyTCU0 device still exists. It does reduce the logging to the debug port but I had that originally in my very first post and it wasn’t enough.

18

Could you share the full flash log for further check?

19

Here is the full flash log:

flash.log (581.3 KB)

20 
copying dtbfile(/home/dmadill/nvidia/nvidia_sdk/JetPack_5.1.1_Linux_JETSON_XAVIER_NX_TARGETS/Linux_for_Tegra/kernel/dtb/tegra194-p3668-0001-p3509-0000.dtb)... done.

Could you share your Linux_for_Tegra/kernel/dtb/tegra194-p3668-0001-p3509-0000.dtb here?

21

OK. I checked the contents of the tegra194-p3668-0001-p3509-0000.dtb file after flashing and my changes were gone. So I redid the test and very carefully confirmed before flashing that my changes were in the dtb file. But after flashing my changes were gone again. So I am going to have to figure out why that’s happening before trying this test again. Sorry for the invalid test.

22

I found the problem and disabled the combined-uart in the tegra194-p3668-0001-p3509-0000.dtb. The net result is that it no longer boots and according to the debug log it ends up in recovery mode, even though I don’t have the force recovery jumper inserted. It does not enter the UEFI shell.

23

Could you try to just disable the node of combined-uart in /boot/dtb/kernel_tegra194-p3668-0001-p3509-0000.dtb?

24

I flashed the system without making any device tree changes (which boots but is obviously lacking our customizations). I then disabled the combined-uart node in /boot/dtb/kernel_tegra194-p3668-0001-p3509-0000.dtb by setting the status=“disabled”. This boots and the /dev/ttyTCU0 device disappears. Also, the debug UART output stops after the MB1, MB2 and L4TLauncher stages (i.e. the Linux O/S is no longer using it). This is good. Now I just have to figure out why trying the same thing in the device-tree source files didn’t work the same way.

25

It’s great to hear this.
Because bootloader(UEFI) and kernel use the same device tree file, it seems disabling combined-uart for UEFI may cause boot issue.
For your use case, you could also let bootloader and kernel using different dtb file by configure them in board config.

26

This makes a lot of sense. Thank you. I have never tried using a different dtb in the board config for the bootloader and kernel before but I will definitely look into it. In the meantime, I will try patching the dtb after making all our customizations (except those I had made to try to disable the debug UART) and see if my UART issues disappear.

27

You could configure them in board configuration file as following.
DTB_FILE is used for kernel
TBCDTB_FILE is used for bootloader(UEFI)

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