# Yocto Kernel Build Note

## do_prepare_recipe_sysroot

*meta/classes/staging.bbclass*

Copy the files into thw individual recipe work directories.

建立 `recipe-sysroot` 以及 `recipe-sysroot-native` directories，做`do_populate_sysroot`時會與這邊的檔案有相依性

## do_symlink_kernsrc

*meta/classes/kernel.bbclass*

有些old style kernel`${S} = ${WORKDIR}/git`，須將這裡的資料移至`${STAGING_KERNEL_DIR}`
Check if `${S}` not equal to `${STAGING_KERNEL_DIR}`, then move `${S}` files to `${STAGING_KERNEL_DIR}`

Aspeed case:
`${S} == ${STAGING_KERNEL_DIR} == build/tmp/work-shared/witherspoon/kernel-source`

## do_kernel_checkout

*meta/classes/kernel-yocto.bbclass*

Go to `${S}` and do git_init (如果.git存在也要再做一次，wierd)，取得所有remote branch name，並checkout `${machine_branch}`

# Create a working tree copy of the kernel by checking out a branch
machine_branch="${@ get_machine_branch(d, "${KBRANCH}" )}"

def get_machine_branch(d, default):
    fetch = bb.fetch2.Fetch([], d)
    for url in fetch.urls:
        urldata = fetch.ud[url]
        parm = urldata.parm
        if "branch" in parm:
            branches = urldata.parm.get("branch").split(',')
            btype = urldata.parm.get("type")
            if btype != "kmeta":
                return branches[0]
	    
    return default

In Aspeed case: `${S} = build/tmp/work-shared/witherspoon/kernel-source`

## do_validate_branches

*meta/classes/kernel-yocto.bbclass*

1. Ensure that the branch is on the locations specified by SRCREV value.
2. Add new branch `$current_branch-orig` and hard reset it for following patching stage.

Aspeed case:
`${SRCREV_machine}` is empty, `${SRCREV}` is defined in meta-aspeed/recipes-kernel/linux/linux-aspeed_git.bb

## do_kernel_metadata

Find kernel metadata **.scc** (Series Configuration Control) configuration fragments, and patches.

Aspeed case:
.scc and the associated cfg path: `meta-phosphor/aspeed-layer/recipes-kernel/linux/linux-aspeed`

For example, phosphor-gpio-keys.scc:

define KFEATURE_DESCRIPTION "Enable gpio-keys"
kconf non-hardware phosphor-gpio-keys.cfg

`KFEATURE_DESCRIPTION`: Description of the fragment
`kconf [hardware|non-hardware] CFG_FILE`: Queue a configuration fragment for merging into the final Linux .config file.

## do_patch

*meta/classes/kernel-yocto.bbclass*

Apply patches from `.kernel-meta/patch.queue`

In Aspeed case:
No patch exists (No .kernel-meta/series path)

## do_kernel_version_sanity_check

meta/classes/kernel.bbclass

Check kernel version.

If the package version `${PV}` matches the kernel being built `${vers}`, then success.

Aspeed case:
`${PV} = 5.4.39+gitAUTOINC+30079d65ac`, `${vers} = 5.4.39`, `${reg} = ^5\.4\.39`

## do_kernel_configme

*meta/classes/kernel-yocto.bbclass*

Search `.kernel-meta/config.queue` and merge to kernel .config

Aspeed case:
merge log: `build/tmp/work-shared/witherspoon/kernel-source/.kernel-meta/cfg/merge_config_build.log`

## do_populate_lic

*meta/classes/license.bbclass*

Write license information for the recipe that is collected later when the image is constructed.

## do_configure

*meta/classes/kernel.bbclass*

execute following command:

KERNEL_CONFIG_COMMAND ?= "oe_runmake_call -C ${S} CC="${KERNEL_CC}" LD="${KERNEL_LD}" O=${B} olddefconfig"

where
`oe_runmake_call` = `make`
`CC` = `arm-openbmc-linux-gnueabi-gcc`
`LD` = `arm-openbmc-linux-gnueabi-ld.bfd`

## do_kernel_configcheck

*meta/classes/kernel-yocto.bbclass*

驗證requested config是否出現在final .config中

Check three paths:

* ${S}/.meta/cfg/mismatch.txt
* specified values did not make it into the kernel's final configuration
* ${S}/.meta/cfg/invalid.cfg
* This BSP sets config options that are not offered anywhere within this kernel
* ${S}/.meta/cfg/redefinition.txt
* This BSP has configuration options defined in more than one config, with differing values

Aspeed case:
invalid.cfg exists --> CONFIG_INPUT_MOUSDEV

## do_compile

*meta/classes/kernel.bbclass*

for typeformake in zImage ; do
    oe_runmake ${typeformake} CC="${KERNEL_CC} $cc_extra " LD="${KERNEL_LD}"
done

where
`$typeformake ` = `zImage`

## do_shared_workdir

編譯kernel結束到編譯lernel module之前，將kernel module的必要檔案移至shared work directory

Aspeed case:

shared work directory = `kerneldir` = `build/tmp/work-shared/witherspoon/kernel-build-artifacts`

## do_kernel_link_images

Do some symbolic link for vmlinux and vmlinuz

## do_assemble_fitimage

meta/class/kernel-fitimage.bbclass

Assemble the fit image

1. Prepare a kernel image section
2. Prepare a DTB image section
3. Prepare a configurations section

## do_compile_kernelmodules

*meta/classes/kernel.bbclass*

Search `CONFIG_MODULES=y` in .config, then make modules

Note:` CONFIG_MODULES` == Enable loadable module support

In Aspeed case:
no modules to compile

## do_strip

*meta/classes/kernel.bbclass*

if `KERNEL_IMAGE_STRIP_EXTRA_SECTIONS` is defined, emove nonessential sections such as .comment sections.

In Aspeed case:
No action

## do_sizecheck

*meta/classes/kernel.bbclass*

If `KERNEL_IMAGE_MAXSIZE` is defined, check kernel size. If size greater than `KERNEL_IMAGE_MAXSIZE`, it will show warning message

In Aspeed case:
`KERNEL_IMAGE_MAXSIZE` not defined

## do_install

*meta/classes/kernel.bbclass/kerneldoinstall()*

Copy kernel modules and fitimage to holding area `${D}`, do_package phase will use this holding directory.

Aspeed case:
No `CONFIG_MODULES=y`, so no modules to install
`${D} = build/tmp/work/witherspoon-openbmc-linux-gnueabi/linux-aspeed/5.4.39+gitAUTOINC+30079d65ac-r0/image`
`${KERNEL_IMAGEDEST} = boot`

## do_package

*meta/classes/package.bbclass*

## do_populate_sysroot

*meta/classes/staging.bbclass*

Copy a subset of the files installed by the do_install task into apporiate sysroot.

execute sysroot_stage_all --> sysroot_strip

## do_packagedata

*meta/classes/package.bbclass*

Saves package metadata generated by the do_package task in `$PKGDATA_DIR` to make it available globally

## do_package_write_rpm

Creates RPM packages (*.rpm) and places them in the `${DEPLOY_DIR_RPM}` directory

Aspeed case:
`${DEPLOY_DIR_RPM}` = `build/tmp/deploy/rpm`

## do_package_qa

*meta/classes/insane.bbclass*

Run QA checks on packaged files.

## do_bundle_initramfs

Combine an initial RAM disk (initramfs) image and kernel together to form a single image

## do_assemble_fitimage_initramfs

Aspeed case:
`$INITRAMFS_IMAGE` is empty, no action.

## do_deploy

Writes output files that are to be deployed to `${DEPLOY_DIR_IMAGE}`

## do_build

The default task for all recipes.

# OpenBMC Image


* aspeed-ast2600a1-evb--5.1.3+git0+3be8a38861-r0-evb-ast2600-20200602032717.dtb
--> kernel dtb file
* aspeed-image-initramfs-evb-ast2600-20200527072154.rootfs.cpio.xz
--> initramfs
* fitImage-aspeed-image-initramfs-evb-ast2600--5.1.3+git0+3be8a38861-r0-evb-ast2600-20200602032717.bin
--> Kernel FIT image (kernel + dtb + initramfs)