[Bug 1846329] Re: [SRU] 2019.07 to support Pi4 boot

[Robie Basak]

After much review discussion I am sponsoring 2019.07+dfsg-1ubuntu4 to
Focal and 2019.07+dfsg-1ubuntu3~18.04.1 to Bionic (I tweaked the
version).

On the Bionic backport, I note that it's essentially impossible to
review all the upstream changes for functional behaviour changes to
users on Bionic, so we will have to rely entirely on QA instead. The
alternative is to not enable Pi 4 on Bionic at all, so on balance this
seems like the only reasonable path forward.

Eoan needs looking at. Some changes from 2019.07+dfsg-1ubuntu3 to
2019.07+dfsg-1ubuntu4 may need backporting in an SRU to Eoan to make
sure the upgrade path Bionic->Eoan->Focal works correctly at both of
those points. I suggest this needs resolving before the Bionic SRU lands
in the updates pocket, but leave that decision to the SRU reviewer.

We also identified a race condition: if flash-kernel is deconfigured to
resolve the Breaks and then upgraded afterwards, flash-kernel won't run
itself. This will be fixed separately in flash-kernel and will need no
further changes to u-boot.

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https://bugs.launchpad.net/bugs/1846329

Title:
  [SRU] 2019.07 to support Pi4 boot

Status in u-boot package in Ubuntu:
  Fix Released
Status in u-boot source package in Bionic:
  In Progress

Bug description:
  Impact
  ======

  The current stable release (bionic) does not support booting on the
  Raspberry Pi 4. Several packages need back-porting from devel to
  support this, along with a new kernel. In addition, there are now
  changes in the back-port that require updates to focal.

  Bionic back-port branch:

  https://code.launchpad.net/~waveform/ubuntu/+source/u-boot/+git/u-boot/+ref
  /bionic-clean-up

  Focal branch:

  https://code.launchpad.net/~waveform/ubuntu/+source/u-boot/+git/u-boot/+ref
  /focal-clean-up

  Builds of packages for both releases available from the following PPA
  (along with all packages required for testing the bionic back-port):

  https://launchpad.net/~waveform/+archive/ubuntu/pi4

  Test Case
  =========

  * Attempt to boot the latest bionic image (18.04.3) on a pi4; note failure
  * Move the SD card to a pi3 and boot successfully
  * Ensure all packages are up to date (apt update/upgrade)
  * sudo add-apt-repository ppa:waveform/pi4
  * sudo apt upgrade
  * sudo reboot
  * Ensure boot proceeds successfully on the pi3
  * Verify facilities (USB peripherals, USB mass storage, wifi, bluetooth, audio, etc.) work
  * sudo apt install linux-image-raspi2-hwe-18.04-edge
  * sudo reboot
  * Ensure boot proceeds successfully on the pi3
  * Verify facilities (USB peripherals, USB mass storage, wifi, bluetooth, audio, etc.) work
  * Move the SD card back to the pi4
  * Ensure boot proceeds successfully on the pi4
  * Verify facilities (USB peripherals, USB mass storage, wifi, bluetooth, audio, etc.) work
  * Repeat for both archs (armhf and arm64)

  Regression Potential
  ====================

  Plenty; pi4 support on bionic requires back-ports of flash-kernel,
  u-boot, linux-firmware-raspi2, and the kernel. Furthermore, the
  firmware package needs to support two kernels (the current 4.x series
  and the proposed 5.x series). Verification of boot, and other
  facilities (USB peripherals, mass storage, free memory, wifi, etc.
  etc.) should be performed on both archs and all supported models of pi
  (2, 3, 3A+, 3B+, 4B all memory variants).

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