** Description changed:

  Currently we have a different boot sequence on the Pi depending on which
  release is used:
  
  * Focal images (and prior) all use u-boot
  
  * Groovy images (and onwards) don't
  
  * However, upgraders from Focal to Groovy aren't forced off u-boot;
  their boot configuration remains untouched
  
  We should update user's boot configuration to migrate them off u-boot if
  they're still on it prior to upgrade to impish. This should be added as
  a quirk to do-release-upgrade. The primary complexity is that the Focal
  boot configuration is split into three files which should be merged.
  Logic from pibootctl's parser can be used for a lot of this.
+ 
+ The specific changes required (for those that wish to perform the
+ changes manually):
+ 
+ * Find "include syscfg.txt" and "include usercfg.txt" and include the
+ content of those files directly in "config.txt" instead.
+ 
+ * Remove/comment out all kernel=uboot_rpi_* lines referring to u-boot
+ (in all conditional sections), and add a kernel=vmlinuz line to the
+ [all] conditional section (adding that section if it's not found).
+ 
+ * Add an "initramfs initrd.img followkernel" line to the [all]
+ conditional section (using the section added by the prior step if
+ required).
+ 
+ * Remove any "device_tree_address=" lines from the configuration.
+ 
+ This switches the sequence from the current one (Pi's native bootloader
+ loads u-boot, which then loads the Linux kernel and the initrd, before
+ passing control to the kernel), to the new one (Pi's native bootloader
+ loads the Linux kernel and the initrd, then passes control to the
+ kernel).
+ 
+ The inlining of the split configuration files deals with a subtle edge
+ case of the early versions of pibootctl being used to set the kernel
+ and/or initrd, and writing those settings into syscfg.txt where they
+ would override our changes. Releases after Focal removed the split (on
+ new images), so this also helps keep the configuration layout
+ consistent.

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https://bugs.launchpad.net/bugs/1936401

Title:
  Migrate Pi users away from u-boot in impish

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