[FAQ] TDA4VM: J721e:/J7200: How to switch console to a different UART instance

Yes. That is possible.

As per the boot flow we have 3 stages.

1. R5 SPL
2. A72 SPL
3. A72 u-boot.

So we need to change at all levels. On top of that ATF(Arm Trusted Firmware) also needs to change the console port as needed.

Following are the dts changes on J7200 & similar changes for J721e will work fine:

diff --git a/arch/arm/dts/k3-j7200-common-proc-board-u-boot.dtsi b/arch/arm/dts/k3-j7200-common-proc-board-u-boot.dtsi
index 207448c4..7a27938a 100644
--- a/arch/arm/dts/k3-j7200-common-proc-board-u-boot.dtsi
+++ b/arch/arm/dts/k3-j7200-common-proc-board-u-boot.dtsi
@@ -5,7 +5,7 @@
 
 / {
 	chosen {
-		stdout-path = "serial2:115200n8";
+		stdout-path = "serial1:115200n8";
 		tick-timer = &timer1;
 	};
 
diff --git a/arch/arm/dts/k3-j7200-common-proc-board.dts b/arch/arm/dts/k3-j7200-common-proc-board.dts
index 423cf546..3ac1e9e3 100644
--- a/arch/arm/dts/k3-j7200-common-proc-board.dts
+++ b/arch/arm/dts/k3-j7200-common-proc-board.dts
@@ -14,8 +14,8 @@
 
 / {
 	chosen {
-		stdout-path = "serial2:115200n8";
-		bootargs = "console=ttyS2,115200n8 earlycon=ns16550a,mmio32,0x02800000";
+		stdout-path = "serial1:115200n8";
+		bootargs = "console=ttyS1,115200n8 earlycon=ns16550a,mmio32,0x40a00000";
 	};
 
 	aliases {
diff --git a/include/configs/j721e_evm.h b/include/configs/j721e_evm.h
index 1a84a68b..c4f4be5f 100644
--- a/include/configs/j721e_evm.h
+++ b/include/configs/j721e_evm.h
@@ -93,8 +93,8 @@
 		"setenv name_fdt ${default_device_tree};"		\
 		"setenv fdtfile ${name_fdt}\0"				\
 	"name_kern=Image\0"						\
-	"console=ttyS2,115200n8\0"					\
-	"args_all=setenv optargs earlycon=ns16550a,mmio32,0x02800000 "	\
+	"console=ttyS1,115200n8\0"					\
+	"args_all=setenv optargs earlycon=ns16550a,mmio32,0x40a00000 "	\
 		"${mtdparts}\0"						\
 	"run_kern=booti ${loadaddr} ${rd_spec} ${fdtaddr}\0"
 
diff --git a/include/environment/ti/boot.h b/include/environment/ti/boot.h
index 9300ec49..d71262d6 100644
--- a/include/environment/ti/boot.h
+++ b/include/environment/ti/boot.h
@@ -10,7 +10,7 @@
 #define __TI_BOOT_H
 
 #ifndef CONSOLEDEV
-#define CONSOLEDEV "ttyS2"
+#define CONSOLEDEV "ttyS1"
 #endif
 
 #define VBMETA_PART_SIZE		(64 * 1024)

The above dts changes take care of the SPL/u-boot side.

Now we also need to change in ATF (Arm Trusted Firmware).

Attached patch needs to be applied on top of ATF directory in the SDK: 

From 54990cac252c3f2eadfd5027198501817f2e5af0 Mon Sep 17 00:00:00 2001
From: Keerthy <j-keerthy@ti.com>
Date: Tue, 23 Mar 2021 21:56:29 +0530
Subject: [PATCH] plat: ti: k3: include: platform_def.h: Change console UART
 from MAIN_UART0 to MCU_UART0

Change console UART from MAIN_UART0 to MCU_UART0.

Signed-off-by: Keerthy <j-keerthy@ti.com>
---
 plat/ti/k3/include/platform_def.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/plat/ti/k3/include/platform_def.h b/plat/ti/k3/include/platform_def.h
index 690c68e5c..db083ca2f 100644
--- a/plat/ti/k3/include/platform_def.h
+++ b/plat/ti/k3/include/platform_def.h
@@ -91,14 +91,14 @@
 
 /* Platform default console definitions */
 #ifndef K3_USART_BASE
-#define K3_USART_BASE 0x02800000
+#define K3_USART_BASE 0x40a00000
 #endif
 
 /* USART has a default size for address space */
 #define K3_USART_SIZE 0x1000
 
 #ifndef K3_USART_CLK_SPEED
-#define K3_USART_CLK_SPEED 48000000
+#define K3_USART_CLK_SPEED 96000000
 #endif
 
 /* Crash console defaults */
-- 
2.17.1

Follow the below instructions to apply and compile:

cd $SDK_PATH/board-support/trusted-firmware-a-2.3
git am 0001-plat-ti-k3-include-platform_def.h-Change-console-UAR.patch.txt
make CROSS_COMPILE=aarch64-linux-gnu- ARCH=aarch64 PLAT=k3 TARGET_BOARD=generic SPD=opteed
cp ./build/k3/generic/release/bl31.bin ../prebuilt-images/
cd ../..
make u-boot
cp board-support/u-boot_build/A72/tispl.bin board-support/u-boot_build/A72/u-boot.img /media/$USER/BOOT

In case you want to avoid compilation of ATF: Just unzip & use the attached binary:


bl31.zip

copy it directly to $SDK_PATH/prebuilt-images

then 'make u-boot' to make the new bl31.bin part of tispl.bin.

Kernel changes for switching console from MAIN_UART0 to MCU_UART

diff --git a/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts b/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts
index 3ac2dab2a..f67fd65af 100644
--- a/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts
+++ b/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts
@@ -15,8 +15,8 @@
 
 / {
 	chosen {
-		stdout-path = "serial2:115200n8";
-		bootargs = "console=ttyS2,115200n8 earlycon=ns16550a,mmio32,0x02800000";
+		stdout-path = "serial1:115200n8";
+		bootargs = "console=ttyS1,115200n8 earlycon=ns16550a,mmio32,0x40a00000";
 	};
 
 	vdd_mmc1: fixedregulator-sd {
@@ -144,6 +144,11 @@
 	power-domains = <&k3_pds 146 TI_SCI_PD_SHARED>;
 };
 
+&mcu_uart0 {
+	power-domains = <&k3_pds 149 TI_SCI_PD_SHARED>;
+	status = "okay";
+};
+
 &main_uart2 {
 	/* MAIN UART 2 is used by R5F firmware */
 	status = "disabled";