1). 简介

嵌入式平台设备基于 Yocto Linux 在开发后期量产前期，为了安全以及提高启动速度等考虑，希望将 ARM 处理器平台的 Debug Console 输出关闭，本文就基于 NXP i.MX8MP ARM 处理器平台来演示相关流程。

本文所示例的平台来自于 Toradex Verdin i.MX8MP 嵌入式平台。

2. 准备

a). Verdin i.MX8MP ARM核心版配合Dahlia 载板并连接 Debug Console 和 HDMI 显示器进行测试。

3). 测试流程

a). 参考这里说明下载 Toradex Yocto Linux BSP7 对应 U-Boot 源码，根据如下 patch 文件修改编译配置后重新编译 U-Boot Image。

-------------------------------

--- a/.config 2024-12-27 14:52:26.151705541 +0800

+++ .b/.config 2025-01-03 17:41:42.779299312 +0800

@@ -535,9 +535,13 @@

 # CONFIG_DISABLE_CONSOLE is not set

 CONFIG_LOGLEVEL=4

 CONFIG_SPL_LOGLEVEL=4

-# CONFIG_SILENT_CONSOLE is not set

-# CONFIG_SPL_SILENT_CONSOLE is not set

+CONFIG_SILENT_CONSOLE=y

+CONFIG_SPL_SILENT_CONSOLE=y

 # CONFIG_TPL_SILENT_CONSOLE is not set

+# CONFIG_SILENT_U_BOOT_ONLY is not set

+CONFIG_SILENT_CONSOLE_UPDATE_ON_SET=y

+CONFIG_SILENT_CONSOLE_UPDATE_ON_RELOC=y

+# CONFIG_SILENT_CONSOLE_UNTIL_ENV is not set

 # CONFIG_PRE_CONSOLE_BUFFER is not set

 CONFIG_CONSOLE_FLUSH_SUPPORT=y

 # CONFIG_CONSOLE_FLUSH_ON_NEWLINE is not set

@@ -644,7 +648,7 @@

 CONFIG_SPL_HAS_CUSTOM_MALLOC_START=y

 CONFIG_SPL_CUSTOM_SYS_MALLOC_ADDR=0x42200000

 CONFIG_SPL_SYS_MALLOC_SIZE=0x80000

-CONFIG_SPL_BANNER_PRINT=y

+# CONFIG_SPL_BANNER_PRINT is not set

 # CONFIG_SPL_DISPLAY_PRINT is not set

 CONFIG_SPL_SYS_MMCSD_RAW_MODE=y

 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR=y

-------------------------------

b). 参考这里说明重新组装 Verdin i.MX8MP Boot Container，在编译 ATF Image 的时候参考如下命令来关闭 log 输出。

-------------------------------

$ make PLAT=imx8mp IMX_BOOT_UART_BASE=0x30880000 LOG_LEVEL=0 DEBUG=0 bl31

-------------------------------

c). 从下面地址下载 Yocto linux BSP7 Minimal/Multimedia Image 并解压。

https://developer.toradex.cn/software/toradex-embedded-software/toradex-download-links-torizon-linux-bsp-wince-and-partner-demos/#bsp-quarterly-releases

d). 用上述步骤 b 生成的 flash.bin binary 文件重命名为 “imx-boot” 并替换 BSP Image 里面的 “imx-boot” 文件。

-------------------------------

$ tar xvf /Verdin-iMX8MP_Reference-Multimedia-Image-Tezi_7.0.0+build.1.tar

$ $ cd/Verdin-iMX8MP_Reference-Multimedia-Image-Tezi_7.0.0+build.1/

$ cp/imx-mkimage/iMX8M/flash.bin/Verdin-iMX8MP_Reference-Multimedia-Image-Tezi_7.0.0+build.1/imx-boot

-------------------------------

e). 参考如下 patch 修改编译 BSP Image 中的环境变量定义文件。

-------------------------------

--- a/u-boot-initial-env-sd 2024-10-01 21:50:32.000000000 +0800

+++ b/u-boot-initial-env-sd 2024-12-27 16:28:20.000000000 +0800

@@ -19,7 +19,7 @@

 bootcmd_mmc1=devnum=1; run mmc_boot

 bootcmd_mmc2=devnum=2; run mmc_boot

 bootdelay=1

-console=ttymxc2

+console=null

 cpu=armv8

 distro_bootcmd=setenv nvme_need_init; for target in ${boot_targets}; do run bootcmd_${target}; done

 efi_dtb_prefixes=/ /dtb/ /dtb/current/

@@ -45,6 +45,7 @@

 scan_dev_for_scripts=for script in ${boot_scripts}; do if test -e ${devtype} ${devnum}:${distro_bootpart} ${prefix}${script}; then echo Found U-Boot script ${prefix}${script}; run boot_a_script; echo SCRIPT FAILED: continuing...; fi; done

 scriptaddr=0x50280000

 soc=imx8m

+silent=1

 update_uboot=askenv confirm Did you load flash.bin (y/N)?; if test "$confirm" = "y"; then setexpr blkcnt ${filesize} + 0x1ff && setexpr blkcnt ${blkcnt} / 0x200; mmc dev 2 1; mmc write ${loadaddr} 0x0 ${blkcnt}; fi

 usb_boot=usb start; if usb dev ${devnum}; then devtype=usb; run scan_dev_for_boot_part; fi

 usb_ignorelist=0x1050:*,

-------------------------------

//当然，U-Boot 环境变量的修改也可以通过修改 U-boot 源代码中 include/configs/verdin-imx8mp.h 文件来修改，本文不做赘述。

// 如果只需要不显示部分 Kernel log 信息，则可以只设置增加如下环境变量即可，无需重新修改编译 U-Boot

-------------------------------

# setenv tdxargs '${tdxargs} quiet'

# saveenv

-------------------------------

f). 参考这里说明将修改的 BSP Image 重新更新到 Verdin i.MX8MP 模块，启动后 Debug Console 输出如下，仅剩下 SPL 配合 ARM 处理器 BootRoM 启动的简单 log 信息输出，其他 U-Boot以及 Linux Kernel/Rootfs 等输出均已经不显示。同时此时测试在不进行任何其他优化的前提下，从按下载板 “Power ON” 按键开机，到连接的 HDMI 屏幕出现 Qt Cinama Demo 应用显示，一共是14s 时间。而正常不做任何修改的 Yocto Linux Multimedia BSP 同样情况启动时间在 17s - 18s。

-------------------------------

DDRINFO: start DRAM init

DDRINFO: DRAM rate 4000MTS

Training FAILED

DDRINFO: start DRAM init

DDRINFO: DRAM rate 4000MTS

DDRINFO:ddrphy calibration done

DDRINFO: ddrmix config done

DDR configured as single rank

SEC0:  RNG instantiated

Normal Boot

WDT:   Started watchdog@30280000 with servicing every 1000ms (60s timeout)

Boot Stage: Primary boot

Find img info 0x4802d200, size 888

Need continue download 1024

Failed to find node!, err: -1!

Failed to find node!, err: -1!

-------------------------------

g). 通常情况上面保留 SPL BootROM 启动相关 log 打印即可满足需求，如果一定要完全去掉，就需要逐项查看对应的源代码，当前打印信息对应（BSP版本变更可能导致变化）以及修改 patch 请见如下，在对应源码中注释掉相关的 “printf()/puts()” 打印 log 输出代码重新编译即可，测试下来这样可以将启动时间缩短到 13.8s 左右。

./ ddr_init.c - https://git1.toradex.com/cgit/u-boot-toradex.git/tree/drivers/ddr/imx/imx8m/ddr_init.c?h=toradex_imx_lf_v2024.04

-------------------------------

DDRINFO: start DRAM init

DDRINFO: DRAM rate 4000MTS

DDRINFO: start DRAM init

DDRINFO: DRAM rate 4000MTS

DDRINFO:ddrphy calibration done

DDRINFO: ddrmix config done

-------------------------------

./ ddrphy_utils.c - https://git1.toradex.com/cgit/u-boot-toradex.git/tree/drivers/ddr/imx/phy/ddrphy_utils.c?h=toradex_imx_lf_v2024.04#n101

-------------------------------

Training FAILED

-------------------------------

./ spl.c - https://git1.toradex.com/cgit/u-boot-toradex.git/tree/board/toradex/verdin-imx8mp/spl.c?h=toradex_imx_lf_v2024.04

-------------------------------

DDR configured as single rank

Normal Boot

-------------------------------

./ jr.c - https://git1.toradex.com/cgit/u-boot-toradex.git/tree/drivers/crypto/fsl/jr.c?h=toradex_imx_lf_v2024.04#n937

-------------------------------

SEC0:  RNG instantiated

-------------------------------

./ wdt-uclass.c - https://git1.toradex.com/cgit/u-boot-toradex.git/tree/drivers/watchdog/wdt-uclass.c?h=toradex_imx_lf_v2024.04#n143

-------------------------------

WDT:   Started watchdog@30280000 with servicing every 1000ms (60s timeout)

-------------------------------

./ spl_imx_romapi.c - https://git1.toradex.com/cgit/u-boot-toradex.git/tree/arch/arm/mach-imx/spl_imx_romapi.c?h=toradex_imx_lf_v2024.04

-------------------------------

Boot Stage: Primary boot

Find img info 0x4802d200, size 888

Need continue download 1024

-------------------------------

./ spl.c - https://git1.toradex.com/cgit/u-boot-toradex.git/tree/arch/arm/mach-imx/spl.c?h=toradex_imx_lf_v2024.04#n459

-------------------------------

Failed to find node!, err: -1!

Failed to find node!, err: -1!

-------------------------------

// 完整修改 patch 请见如下

-------------------------------

diff --git a/arch/arm/mach-imx/spl.c b/arch/arm/mach-imx/spl.c

index d6664bf9103..a8ef680593b 100644

--- a/arch/arm/mach-imx/spl.c

+++ b/arch/arm/mach-imx/spl.c

@@ -456,7 +456,7 @@ int board_handle_rdc_config(void *fdt_addr, const char *config_name, void *dst_a

  node = fdt_node_offset_by_compatible(fdt_addr, -1, "imx8m,mcu_rdc");

  if (node < 0) {

-  printf("Failed to find node!, err: %d!\n", node);

+  //printf("Failed to find node!, err: %d!\n", node);

   ret = -1;

   goto exit;

  }

diff --git a/arch/arm/mach-imx/spl_imx_romapi.c b/arch/arm/mach-imx/spl_imx_romapi.c

index 8b8d16d911f..fea293cb9ca 100644

--- a/arch/arm/mach-imx/spl_imx_romapi.c

+++ b/arch/arm/mach-imx/spl_imx_romapi.c

@@ -387,7 +387,7 @@ static int spl_romapi_load_image_stream(struct spl_image_info *spl_image,

  }

  imagesize = img_info_size(phdr);

- printf("Find img info 0x%p, size %d\n", phdr, imagesize);

+ //printf("Find img info 0x%p, size %d\n", phdr, imagesize);

  if (p - phdr < imagesize) {

   imagesize -= p - phdr;

@@ -463,11 +463,11 @@ int board_return_to_bootrom(struct spl_image_info *spl_image,

  if (ret != ROM_API_OKAY)

   goto err;

- printf("Boot Stage: ");

+ //printf("Boot Stage: ");

  switch (bstage) {

  case BT_STAGE_PRIMARY:

-  printf("Primary boot\n");

+  //printf("Primary boot\n");

   break;

  case BT_STAGE_SECONDARY:

   printf("Secondary boot\n");

diff --git a/board/toradex/verdin-imx8mp/spl.c b/board/toradex/verdin-imx8mp/spl.c

index 73729a42b45..f6bf9260527 100644

--- a/board/toradex/verdin-imx8mp/spl.c

+++ b/board/toradex/verdin-imx8mp/spl.c

@@ -42,7 +42,7 @@ void spl_dram_init(void)

  lpddr4_single_rank_training_patch();

  if (!ddr_init(&dram_timing)) {

-  puts("DDR configured as single rank\n");

+  //puts("DDR configured as single rank\n");

   return;

  }

  puts("DDR configuration failed\n");

@@ -69,7 +69,7 @@ void spl_board_init(void)

  clock_set_target_val(GIC_CLK_ROOT, CLK_ROOT_ON | CLK_ROOT_SOURCE_SEL(5));

  clock_enable(CCGR_GIC, 1);

- puts("Normal Boot\n");

+ //puts("Normal Boot\n");

 }

 #define I2C_PAD_CTRL (PAD_CTL_DSE6 | PAD_CTL_HYS | PAD_CTL_PUE | PAD_CTL_PE)

diff --git a/drivers/crypto/fsl/jr.c b/drivers/crypto/fsl/jr.c

index 97b0cf83ae7..efb2544de02 100644

--- a/drivers/crypto/fsl/jr.c

+++ b/drivers/crypto/fsl/jr.c

@@ -934,7 +934,7 @@ init:

    return -1;

   }

-  printf("SEC%u:  RNG instantiated\n", sec_idx);

+  //printf("SEC%u:  RNG instantiated\n", sec_idx);

  }

 #if CONFIG_IS_ENABLED(OF_CONTROL)

  if (CONFIG_IS_ENABLED(DM_RNG)) {

diff --git a/drivers/ddr/imx/imx8m/ddr_init.c b/drivers/ddr/imx/imx8m/ddr_init.c

index 91d963419d6..06ff6feaa09 100644

--- a/drivers/ddr/imx/imx8m/ddr_init.c

+++ b/drivers/ddr/imx/imx8m/ddr_init.c

@@ -316,7 +316,7 @@ int ddr_init(struct dram_timing_info *dram_timing)

  unsigned int tmp, initial_drate, target_freq;

  int ret;

- printf("DDRINFO: start DRAM init\n");

+ //printf("DDRINFO: start DRAM init\n");

  /* Step1: Follow the power up procedure */

  if (is_imx8mq()) {

@@ -339,7 +339,7 @@ int ddr_init(struct dram_timing_info *dram_timing)

  initial_drate = dram_timing->fsp_msg[0].drate;

  /* default to the frequency point 0 clock */

- printf("DDRINFO: DRAM rate %dMTS\n", initial_drate);

+ //printf("DDRINFO: DRAM rate %dMTS\n", initial_drate);

  ddrphy_init_set_dfi_clk(initial_drate);

  /* D-aasert the presetn */

@@ -409,7 +409,7 @@ int ddr_init(struct dram_timing_info *dram_timing)

   tmp = reg32_read(DDRPHY_CalBusy(0));

  } while ((tmp & 0x1));

- printf("DDRINFO:ddrphy calibration done\n");

+ //printf("DDRINFO:ddrphy calibration done\n");

  /* Step15: Set SWCTL.sw_done to 0 */

  reg32_write(DDRC_SWCTL(0), 0x00000000);

@@ -462,7 +462,7 @@ int ddr_init(struct dram_timing_info *dram_timing)

  /* enable port 0 */

  reg32_write(DDRC_PCTRL_0(0), 0x00000001);

- printf("DDRINFO: ddrmix config done\n");

+ //printf("DDRINFO: ddrmix config done\n");

  board_dram_ecc_scrub();

diff --git a/drivers/ddr/imx/phy/ddrphy_utils.c b/drivers/ddr/imx/phy/ddrphy_utils.c

index 59a15764526..cddf270e594 100644

--- a/drivers/ddr/imx/phy/ddrphy_utils.c

+++ b/drivers/ddr/imx/phy/ddrphy_utils.c

@@ -98,7 +98,7 @@ int wait_ddrphy_training_complete(void)

    debug("Training PASS\n");

    return 0;

   } else if (mail == 0xff) {

-   printf("Training FAILED\n");

+   //printf("Training FAILED\n");

    return -1;

   }

  }

diff --git a/drivers/watchdog/wdt-uclass.c b/drivers/watchdog/wdt-uclass.c

index 417e8d7eef9..7e4213858b8 100644

--- a/drivers/watchdog/wdt-uclass.c

+++ b/drivers/watchdog/wdt-uclass.c

@@ -140,9 +140,9 @@ int wdt_start(struct udevice *dev, u64 timeout_ms, ulong flags)

    }

   }

-  printf("WDT:   Started %s with%s servicing %s (%ds timeout)\n",

+  /*printf("WDT:   Started %s with%s servicing %s (%ds timeout)\n",

          dev->name, IS_ENABLED(CONFIG_WATCHDOG) ? "" : "out",

-         str, (u32)lldiv(timeout_ms, 1000));

+         str, (u32)lldiv(timeout_ms, 1000));*/

  }

  return ret;

-------------------------------

h). 另外，U-Boot 默认的 countdown 功能虽然没有打印 log 了，但是还是依然存在，可以通过如下修改 u-boot-initial-env-sd 环境变量配置来忽略这个功能。设置后可以将启动时间缩短为 12s - 13s。

-------------------------------

bootdelay=-2

// bootdelay variable description from U-Boot documentation

bootdelay: After reset, U-Boot will wait this number of seconds before it executes the contents of the bootcmd variable. During this time a countdown is printed, which can be interrupted by pressing any key.

Set this variable to 0 boot without delay. Be careful: depending on the contents of your bootcmd variable, this can prevent you from entering interactive commands again forever!

Set this variable to -1 to disable autoboot.

Set this variable to -2 to boot without delay and not check for abort.

-------------------------------

4). 总结

本文基于 NXP i.MX8MP ARM 处理器平台测试了关闭 Debug Console 来增强安全和提高启动时间的流程。

参考文档

https://developer.toradex.com/software/development-resources/configuring-serial-port-debug-console-linuxu-boot/

如需了解更多信息,请访问 (韬睿（上海）计算机科技有限公司)官网 http://www.toradex.com