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Example: Providing custom u-boot-fw-utils

In this section we list a practical example of how to port a bitbake u-boot recipe to a u-boot-fw-utils recipe. The latter is needed for Mender to operate correctly, but is often omitted when a custom U-Boot fork is made.

For this example we assume that the U-Boot fork in question has a u-boot_<version>.bb file. For our purpose we will use the stock u-boot recipe from the Yocto Project (u-boot_2016.03.bb at the time of writing), and port this to a recipe that produces the u-boot-fw-utils tools.

Example setup

The example setup is only here for completeness' sake, to show how we did the example, and are not relevant if you're porting a real u-boot recipe. Feel free to proceed to the next section if this one doesn't apply to you.

First we create a new folder inside our private bitbake layer:

cd meta-my-layer
mkdir -p recipes-bsp/u-boot-my-fork

Then we copy the u-boot recipe from the Yocto Project:

cp ../meta/recipes-bsp/u-boot/u-boot_2016.03.bb recipes-bsp/u-boot-my-fork_2016.03.bb

In addition we need to change a few things inside the file. Expressed as a diff, this is the change:

--- ../meta/recipes-bsp/u-boot/u-boot_2016.03.bb    2016-07-07 13:46:25.202889701 +0200
+++ recipes-bsp/u-boot-my-fork/u-boot-my-fork_2016.03.bb    2016-11-01 11:05:35.805292065 +0100
@@ -1,4 +1,5 @@
-require u-boot.inc
+require recipes-bsp/u-boot/u-boot.inc
+require recipes-bsp/u-boot/u-boot-mender.inc

 DEPENDS += "dtc-native"

The first line changes a path inside the recipe, since the include file is not in the same directory anymore. The second adds Mender specific tweaks, as described in this section.

Preparations

Start by copying the u-boot recipe file to a new file for the fw-utils, like this:

cd meta-my-layer/recipes-bsp/u-boot-my-fork
cp u-boot-my-fork_2016.03.bb u-boot-fw-utils-my-fork_2016.03.bb

Using the fork

Then, in accordance with this section, we add the following to our configuration:

PREFERRED_PROVIDER_u-boot-fw-utils = "u-boot-fw-utils-my-fork"

For this example we add it to local.conf, but in a real situation it may be more appropriate to add this to the machine.conf file for the board in question.

Adapting the recipe

Here is the complete set of changes made to the recipe, expressed as a diff. We will go through each line and explain why they are needed.

--- u-boot-my-fork_2016.03.bb   2016-11-01 11:42:06.143094834 +0100
+++ u-boot-fw-utils-my-fork_2016.03.bb  2016-11-01 10:19:43.940934880 +0100
@@ -1,7 +1,10 @@
-require recipes-bsp/u-boot/u-boot.inc
-require recipes-bsp/u-boot/u-boot-mender.inc
+require recipes-bsp/u-boot/u-boot-fw-utils-mender.inc

-DEPENDS += "dtc-native"
+SUMMARY = "U-Boot bootloader fw_printenv/setenv utilities"
+LICENSE = "GPLv2+"
+LIC_FILES_CHKSUM = "file://Licenses/README;md5=a2c678cfd4a4d97135585cad908541c6"
+SECTION = "bootloader"
+DEPENDS = "mtd-utils"

 # This revision corresponds to the tag "v2016.03"
 # We use the revision in order to avoid having to fetch it from the
@@ -9,3 +12,30 @@
 SRCREV = "df61a74e6845ec9bdcdd48d2aff5e9c2c6debeaa"

 PV = "v2016.03+git${SRCPV}"
+
+SRC_URI = "git://git.denx.de/u-boot.git;branch=master"
+
+S = "${WORKDIR}/git"
+
+INSANE_SKIP_${PN} = "already-stripped"
+EXTRA_OEMAKE_class-target = 'CROSS_COMPILE=${TARGET_PREFIX} CC="${CC} ${CFLAGS} ${LDFLAGS}" V=1'
+
+inherit uboot-config
+
+do_compile () {
+   oe_runmake ${UBOOT_MACHINE}
+   oe_runmake env
+}
+
+do_install () {
+   install -d ${D}${base_sbindir}
+   install -d ${D}${sysconfdir}
+   install -m 755 ${S}/tools/env/fw_printenv ${D}${base_sbindir}/fw_printenv
+   install -m 755 ${S}/tools/env/fw_printenv ${D}${base_sbindir}/fw_setenv
+   install -m 0644 ${S}/tools/env/fw_env.config ${D}${sysconfdir}/fw_env.config
+}
+
+PACKAGE_ARCH = "${MACHINE_ARCH}"
+
+PROVIDES_${PN} = "u-boot-fw-utils"
+RPROVIDES_${PN} = "u-boot-fw-utils"
  1. We remove the reference to u-boot.inc, because this file is only relevant for the main u-boot recipe, not for u-boot-fw-utils.

  2. We replace u-boot-mender.inc with u-boot-fw-utils-mender.inc. This is because the fw-utils tools requires different tweaks, as described in this section.

  3. The next block of variable assignments (starting with SUMMARY) is added because this normally is provided by u-boot.inc, but since this file is not included anymore, we need to add these variables manually.

  4. We next add the SRC_URI variable, since this also was present in u-boot.inc. Most likely this variable will already exist if the recipe was copied from a real fork of U-Boot, and will likely be different from our example. Using the one from u-boot-my-fork_2016.03.bb should be fine.

  5. The S variable is added since it is missing after u-boot.inc was removed, and the build recipe expects the source directory to be structured like this.

  6. INSANE_SKIP_${PN} is added because u-boot-fw-utils's build process strips the binaries automatically, and unless we add this option, Bitbake will complain if the binaries are already stripped.

  7. EXTRA_OEMAKE_class-target is added because U-Boot needs these environment variables in order to cross compile correctly for our board.

  8. inherit uboot-config makes sure that the Bitbake variables for U-Boot are set correctly. Normally this is inherited by u-boot.inc, but we are not using it in this recipe.

  9. The do_compile block is the heart of our u-boot-fw-utils recipe, and the key difference from the original recipe for u-boot is that we compile the env target. This will compile the fw-utils tools.

  10. The do_install block needs to be defined because naturally, the u-boot-fw-utils recipe needs to have a different set of installables than u-boot, otherwise they would overlap. The three components needed are the two binary tools, fw_printenv and fw_setenv, as well as the configuration file, fw_env.config, which tells said tools where to find the U-Boot environment.

  11. PACKAGE_ARCH is set to ${MACHINE_ARCH} because this recipe will produce binaries that are specific to this board, and not to the architecture in general. This stems from the highly board specific nature of U-Boot. See the official Yocto Project documentation for more information.

  12. The last two PROVIDES_${PN} and RPROVIDES_${PN} variables are added to describe to Bitbake that this recipe provides those packages, even though it has a different name. This is described here.

And that's it! This provides a working recipe for u-boot-fw-utils.

You may notice that the file looks very similar to the one that already exists in the Yocto Project, under meta/recipes-bsp/u-boot/u-boot-fw-utils_2016.03.bb, and this is indeed the case. Much of the inspiration was taken from there, and this is a good place to look if you hit problems and this guide doesn't provide the answer.

After the adaptation is complete, you should go through the Integration checklist to make sure that all functionality of the compiled tools is working.