[FS#3540] ip6806x serial console is mute once kernel takes control (r15355-19d7e73ecc)

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FS#3540 - ip6806x serial console is mute once kernel takes control (r15355-19d7e73ecc)
User who did this - Hannu Nyman (hnyman)

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I did some further debugging, and noticed something:

I compared the kernel build log with the working code (without CONFIG_CMDLINE_OVERRIDE=y) to log with the faulty code, and there is only a small difference:

In the faulty version, there is a one-line warning:
  warning: override: CMDLINE_OVERRIDE changes choice state

context:

  HOSTCC  scripts/kconfig/symbol.o
  HOSTLD  scripts/kconfig/conf
scripts/kconfig/conf  --syncconfig Kconfig
net/sched/Kconfig:45: warning: menuconfig statement without prompt
.config:987:warning: override: CMDLINE_OVERRIDE changes choice state
  HOSTCC  scripts/dtc/dtc.o


So, the new option changes something else.

I looked at build_dir/target-arm_cortex-a15+neon-vfpv4_musl_eabi/linux-ipq806x_generic/linux-5.4.85/arch/arm/Kconfig and noticed that the new definition of CONFIG_CMDLINE_OVERRIDE has been placed into end of a multi-option choice block. Enabling this option may now change the selected value of the choice of ARM_ATAG_DTB_COMPAT_CMDLINE... options.


choice
        prompt "Kernel command line type" if ARM_ATAG_DTB_COMPAT
        default ARM_ATAG_DTB_COMPAT_CMDLINE_FROM_BOOTLOADER

config ARM_ATAG_DTB_COMPAT_CMDLINE_FROM_BOOTLOADER
        bool "Use bootloader kernel arguments if available"
        help
          Uses the command-line options passed by the boot loader instead of
          the device tree bootargs property. If the boot loader doesn't provide
          any, the device tree bootargs property will be used.

config ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND
        bool "Extend with bootloader kernel arguments"
        help
          The command-line arguments provided by the boot loader will be
          appended to the the device tree bootargs property.

config ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE
        bool "Append rootblock parsing bootloader's kernel arguments"
        help
          The command-line arguments provided by the boot loader will be
          appended to a new device tree property: bootloader-args.
          If there is a property "append-rootblock" in DT under /chosen
          and a root= option in bootloaders command line it will be parsed
          and added to DT bootargs with the form: XX.
          Only command line ATAG will be processed, the rest of the ATAGs
          sent by bootloader will be ignored.

config CMDLINE_OVERRIDE
    bool "Use alternative cmdline from device tree"
    help
      Some bootloaders may have uneditable bootargs. While CMDLINE_FORCE can
      be used, this is not a good option for kernels that are shared across
      devices. This setting enables using "chosen/cmdline-override" as the
      cmdline if it exists in the device tree.

endchoice

config CMDLINE
        string "Default kernel command string"
        default ""
        help
          On some architectures (EBSA110 and CATS), there is currently no way


Apparently the new selected option in the block changes the selection of the existing options, causing bugs to other devices depending on those selections. Asrock router apparently is not affected by that change, 

Likely the new code should be after the "endchoice" line, so that ARM_ATAG_DTB_COMPAT_CMDLINE... things do not change.

Or possibly it should be inside the next choice block about CMDLINE:


config CMDLINE
        string "Default kernel command string"
        default ""
        help
          On some architectures (EBSA110 and CATS), there is currently no way
          for the boot loader to pass arguments to the kernel. For these
          architectures, you should supply some command-line options at build
          time by entering them here. As a minimum, you should specify the
          memory size and the root device (e.g., mem=64M root=/dev/nfs).

choice
        prompt "Kernel command line type" if CMDLINE != ""
        default CMDLINE_FROM_BOOTLOADER
        depends on ATAGS

config CMDLINE_FROM_BOOTLOADER
        bool "Use bootloader kernel arguments if available"
        help
          Uses the command-line options passed by the boot loader. If
          the boot loader doesn't provide any, the default kernel command
          string provided in CMDLINE will be used.

config CMDLINE_EXTEND
        bool "Extend bootloader kernel arguments"
        help
          The command-line arguments provided by the boot loader will be
          appended to the default kernel command string.

config CMDLINE_FORCE
        bool "Always use the default kernel command string"
        help
          Always use the default kernel command string, even if the boot
          loader passes other arguments to the kernel.
          This is useful if you cannot or don't want to change the
          command-line options your boot loader passes to the kernel.
endchoice


Kernel & bootloader option specialists may take a closed look, but I think that this might well be the reason.

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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=3540#comment9244

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