[yocto] using BBMULTICONFIG to create a 32-bit rootfs, kernel, u-boot that also includes a 64-bit kernel, u-boot for NXP i.mx6/i.mx8

[Joshua Watt]

On 10/15/19 2:03 PM, Davis Roman wrote:
> Hi Joshua,
>
> Thank you for replying.
>
> Since my last email, I enabled BBMULTICONFIG and was able to build 
> both 32bit and 64bit machine types successfully and so i have both 
> packages available in their corresponding build folders.
>
> build/tmp-imx6sxsabresd/deploy/rpm/imx6sxsabresd/kernel-4.14.98-r0.imx6sxsabresd.rpm
> build/tmp-imx8mmevk/deploy/rpm/imx8mmevk/kernel-4.14.98-r0.imx8mmevk.rpm
>
> I checked out mcdepends however I don't believe this helps me to do 
> the last piece which is to pull the 64-bit kernel package into my 
> 32-bit image.
> According to the yocto docs, mcdepends ensures that imageA is built 
> only after imageB has finished building (or at least that's how I 
> understand it).

The documentation might be a little misleading; mcdepends allows a 
*task* from one multiconfig to depend on a *task* from another. Using 
the image creation task (do_rootfs) is just an example.

I think one way to do what you want is write a recipe that mcdepends on 
the do_deploy task from the 64-bit kernel recipe, pulls the deployed 
kernel image, repackage it, and then install that recipe's package into 
the 32-bit rootfs. There might be other ways that someone knows about 
that would be better/cleaner, but that's what I would do.

>
> In parallel, I'm studying a patch that was upstreamed in 2017 for 
> adding support for multiple kernel packages 
> (http://lists.openembedded.org/pipermail/openembedded-core/2017-October/143674.html)
> This appears to be in line with what I'm looking to do however the 
> wrinkle is that I'm dealing with two kernels from two different 
> machine types whereas the patch dealt with two kernels of the same 
> machine type.
> I'm still trying to understand the implications of this. My feeling is 
> that I need a hybrid approach of bbmulticonfig and the above patch for 
> adding multiple kernel packages.

Ya, you might be able to do that if your new recipes looks like a kernel 
"flavor" described in that patch.... I'm not quite clear on what the 
advantage of doing that in this case would be; not that there isn't one 
to be had, I just can't see it with a cursory glance :).

>
> Please let me know if you have any thoughts.
>
> Thanks,
>
> Davis
>
> On Fri, Oct 4, 2019 at 10:59 PM Joshua Watt <jpewhacker at gmail.com 
> <mailto:jpewhacker at gmail.com>> wrote:
>
>
>
>     On Fri, Oct 4, 2019, 7:04 PM Davis Roman <davis.roman84 at gmail.com
>     <mailto:davis.roman84 at gmail.com>> wrote:
>
>         Hello,
>
>         We're working on a Linux distro for two systems where one is
>         based on
>         NXP i.mx6(32-bit,armv7) and the other i.mx8(64-bit,armv8).
>
>         I have two machine types defined in Yocto so individually I
>         can build
>         either one however our goal is to create a single distro that
>         can run on both processors.
>
>         So the idea is to use
>         BBMULTICONFIG(https://www.yoctoproject.org/docs/latest/ref-manual/ref-manual.html#var-BBMULTICONFIG)
>
>         to build two separate images,
>
>         1) a 32-bit distro for an i.mx6
>         2) a 64-bit distro for an i.mx8
>
>         and then finally, take the 32-bit distro and add the 64-bit
>         kernel+modules and u-boot.
>
>         ---------------------------------------
>         |--------------------------------------|
>         ||           32-bit rootfs            ||
>         |--------------------------------------|
>         |-----------------   ----------------- |
>         || 32-bit kernel |   |  64-bit kernel ||
>         |-----------------   ----------------- |
>         |-----------------   ----------------- |
>         || 32-bit u-boot |   |  64-bit u-boot ||
>         |-----------------   ----------------- |
>         ---------------------------------------
>            i.mx6solo             i.mx8m mini
>
>         We've already tried our existing 32-bit rootfs + 64-bit
>         kernel/u-boot on the i.mx8 and the system runs.
>         So in theory, it should just be a matter of getting yocto to
>         assemble all the pieces together.
>
>         I don't have much experience with BBMULTICONFIG so any ideas
>         or comments on how to proceed would be appreciated.
>
>
>     You are on the right track. Create two multiconfig files one for
>     each machine, then user mcdepends
>     (https://www.yoctoproject.org/docs/current/mega-manual/mega-manual.html#dev-enabling-multiple-configuration-build-dependencies)
>     to pull the 64 bit kernel, etc. into the 32 bit image.
>
>     BBMULTICONFIG is used in local.conf to select which multiconfigs
>     you want to enable. In your case it would have to list both of the
>     ones that you define.
>
>
>         Thank you,
>
>         Davis
>         -- 
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