Linux kernel Configuration resolution-Boot options

1. Preface

This article describes the configuration items that are related to Linux kernel and startup under the ARM64 architecture.

NOTE 1: The Linux kernel version used in this article series is " X Project "The use of" Linux 4.6-RC5 ", for specific reference" Https://github.com/wowotechX/linux.git ".

2. kconfig file

The configuration items in the ARM64 schema that are related to boot are very simple, mainly including ACPI, command-line parameters, and Uefi. These configuration items are located in "Arch/arm64/kconfig", as follows:

  1:menu "Boot Options"

  3:config Arm64_acpi_parking_protocol

  4:bool "Enable support for theARM64 ACPI Parking Protocol"

  5:depends on ACPI

  6:help

  7: For the   ARM64 ACPI Parking protocol. If Disabled

  8: The kernel won't allow   booting through the ARM64 ACPI parking

  9:   If the corresponding data is present in the ACPI

Ten:   Madt table.

12:config CmdLine

13:string "Default kernel command string"

Default ""

15:help

: Time by   

:   entering them here. As a minimum, you should specify the

:   root device (e.g. Root=/dev/nfs).

20:config Cmdline_force

21:bool "Always use thedefault kernel command string"

22:help

:   if the boot

:   loader passes and arguments to the kernel.

:   If you cannot or don ' t want

:   Command-Line options your boot loader passes to the kernel.

28:config efi_stub

29:bool

31:config EFI

32:bool "UEFI Runtime Support"

33:depends on &&! Cpu_big_endian

34:select LIBFDT

35:select ucs2_string

36:select EFI_PARAMS_FROM_FDT

37:select efi_runtime_wrappers

38:select efi_stub

39:select efi_armstub

Default Y

41:help

: For   runtime services provided

:   by UEFI firmware (suchas non-volatile variables, realtime

:           clock, and platform reset). A UEFI stub is also provided to

The kernel to is booted as an   EFI application. This

Useful on systems, which has   UEFI firmware.

48:config DMI

49:bool "Enable support for SMBIOS (DMI) tables"

50:depends on EFI

Default Y

52:help

: For   systems.

A: This option is only useful on systems and that has the   UEFI firmware.

   However, even with this option, the resultant kernel should

£ º   continue to boot on existing NON-UEFI platforms.

59:endmenu

3. Configuration Item Description

Note 2:linux Kernel's configuration items are numerous, but most of them use the default values. Therefore, in the process of kernel transplant and development, the real need to care is not particularly much. For commonly used configuration items that need to be cared for, I'll mark them with a yellow background in the analysis article.

3.1 ACPI-related configuration items

Configuration Items	Description	Default value
Config_arm64_acpi_ Parking_protocol	Whether to support "ARM64 ACPI Parking Protocol". With regard to ACPI and parking protocol, there are opportunities to analyze in other articles, and there is no need to pay much attention.	dependent on the CONFIG_ACPI

3.2 Configuration items related to kernel command line arguments

Configuration Items	Description	Default value
Config_cmdline	Kernel default command-line arguments. After setting this parameter, you can not need bootloader delivery (it is useful to start porting kernel, because bootloader can not be guaranteed to pass ^_^ correctly)	No
Config_cmdline_force	Enforces the kernel's default command-line arguments (which can be ignored by bootloader), and is typically used to test some new command-line arguments (without modifying the content passed by bootloader) during kernel development.	No

Note 3: If Kconfig does not specify a default value for a configuration item through the "default" keyword, then the configuration item will not appear in the generated. config file, which is "forbidden" in disguise. After the same.

3.3 Uefi-related configuration items

Dmi

Configuration Items	Description	Default value
Config_efi_stub	Used to support EFI boot; After enabling the configuration item, the Kenrel Bzimage header is modified to turn the kernel image into a pe/coff image that can be run by EFI. Refer to the Documentation/efi-stub.txt for details.	No
Config_efi	Supports some runtime services provided by Uefi Firmware, such as RTC, reset, etc., which depend on open Firmware and have a number of associated items (you can refer to the SELECT keyword in the kconfig file); In addition, it is interesting to refer to the "Depends on &&!" in the 2nd chapter of the Kconfig file. Cpu_big_endian "), the configuration item can only be used in the small-end CPU. Be free to study why.	Y
Config_dmi	Used to control whether "SMBIOS/DMI feature" is supported, depending on config_efi, it is important to note that, even if the configuration item is enabled, kernel needs to be able to start normally in other non-UEFI environments.	Y

4. Reference documentation

[1] uefi,http://www.wowotech.net/armv8a_arch/uefi.html

[2] Acpi,https://zh.wikipedia.org/zh-cn/%e9%ab%98%e7%ba%a7%e9%85%8d%e7%bd%ae%e4%b8%8e%e7%94%b5%e6%ba%90%e6%8e%a5%e5%8f%a3

[3] Smbios/dmi,http://www.dmtf.org/cn/standards/smbios

Linux Kernel Configuration resolution-Boot options