[mozilla-flame] Append `dtb` file to `boot.img` (qcdt)

Created by: ollieparanoid

From what @yuvadm told us in the channel, the flame comes with its own version of fastboot/mkbootimg, which appends the dtb file at the end of the boot.img (and not at the end of the kernel, as it is with all other Android devices). The kernel is part of the boot.img file though.

I'm not sure what the best way would be to handle this right now (suggestions welcome!) - @yuvadm, could you point us to the source code of these mozilla specific forks?

@ollieparanoid Thanks for opening an issue on this topic. Also CC'ing @z3ntu here as well since he provided some initial patches.

Essentially we need to pick a mkbootimg that supports the --dt flag which is able to append the device tree files to the boot.img. This is needed not only for the Flame but also for another device I believe @z3ntu is working on porting.

There are several different patched mkbootimg floating around, I'll paste a few that I ran into here, and then we can decide on the merits of each one:

• https://github.com/efidroid/build/blob/master/tools/mkbootimg
• https://github.com/LineageOS/android_system_core/blob/cm-14.1/mkbootimg/mkbootimg

(tbh I'm not exactly sure which version is used by B2G, but I guess it doesn't really matter, we need something that works for many devices)

Once we figure this out, we need to conditionally add the --dt flag to mkbootimg. An initial breaking patch looks like this:

--- a/aports/postmarketos-mkinitfs/mkinitfs.sh
+++ b/aports/postmarketos-mkinitfs/mkinitfs.sh
@@ -171,6 +171,7 @@ create_bootimg()
                --ramdisk_offset "${deviceinfo_flash_offset_ramdisk}" \
                --tags_offset "${deviceinfo_flash_offset_tags}" \
                --pagesize "${deviceinfo_flash_pagesize}" \
+               --dt "${kernelfile/initramfs-/dt.img-}" \
                -o "${outfile/initramfs-/boot.img-}"
 }

By Yuval Adam on 2017-08-02T17:51:59

I have a version of the last patch on my laptop which is non-breaking but I'm on my phone atm

By Luca Weiss on 2017-08-02T18:43:02

Also the method used is called qcdt and I would use the lineage source of the tools if available. @m1cha pushed the important changes from efidroid to Lineage

By Luca Weiss on 2017-08-02T18:46:20

@z3ntu good to know! Would love to get the updated version whenever you have a chance to post it. Also curious if this worked for you. I'm still running into problems with the flame dt.img.

By Yuval Adam on 2017-08-02T18:48:31

Created by: ollieparanoid

Alright, then I suggest to integrate it the following way:

• Replace the mkbootimg we have packaged with the version from LineageOS
• Modify linux-mozilla-flame to save the dtb file in /usr/share/dtb
• Specify the dtb file name in the deviceinfo
• Add a new option: deviceinfo_bootimg_qcdt="true"
• Modify mkinitfs.sh to use the --dt flag, when that option is enabled
• Test if everything works
• Make a PR
• Document the new deviceinfo option in the deviceinfo reference

By * postmarketOS Bot on 2017-08-12T02:44:53

@yuvadm I only got pmOS to boot with a kernel not built via the alpine build process (but normal Android mka zImage)

By Luca Weiss on 2017-08-03T05:49:44

A crude version of that patch is https://github.com/z3ntu/pmbootstrap/commit/6b5a9de46b92fe4edf09a3de6fd65b313b0306f2 but it isn't in the format that @ollieparanoid proposed. I don't really have time this week but next week I should be able to do the things listed (except someone else does them earlier)

By Luca Weiss on 2017-08-03T06:01:13

Created by: ollieparanoid

Support for this feature has been merged in #356, which also shows how to use it. I have extended the deviceinfo reference and added a new sub-article for deviceinfo_bootimg_qcdt (which has not much content yet, but it's a start).

The only thing I would like to see improved in hindsight (you know, after I reviewed the PR and merged it :p) is saving the dt.img file as dt.img-$FLAVOR, so we could have multiple kernels installed in parallel. But we can leave that for another PR if this becomes an issue.

Thanks for working on this feature, this is a great enhancement!

By * postmarketOS Bot on 2017-08-12T03:06:57