[Bug 1847500] Re: Full RAM on Pi4 isn't accessible when using u-boot

[Dave Jones]

@satmandu thanks for the information! I'd got as far as figuring out the
dram_init call was getting the available RAM info from the mailbox,
which only permitted a single bank to be reported, which was then
getting used in the fdt fixup called by the bootm. As it happens the fdt
/memory node was already correct so there was no need for that
particular fixup. Hence the hack applied for now is just to disable the
fdt fixup.

Bumping to 2019.10 would be ideal, but unfortunately it's now too late
in the cycle before release to re-test all the other platforms using
u-boot. Still, it's useful to know that I can scrub that hack when we
bump to 2019.10 (which we can probably do next cycle) - saves me digging
further into it!

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https://bugs.launchpad.net/bugs/1847500

Title:
  Full RAM on Pi4 isn't accessible when using u-boot

Status in Release Notes for Ubuntu:
  Invalid
Status in u-boot package in Ubuntu:
  Fix Released
Status in u-boot source package in Eoan:
  Fix Released

Bug description:
  Booting the latest eoan daily on a Pi4 with >1Gb of RAM, only the
  first 1Gb of RAM appears accessible:

      ubuntu at ubuntu:~$ free
                    total        used        free      shared  buff/cache   available
      Mem:         931920      185484      504748        3664      241688      723820
      Swap:             0           0           0

  However, adjusting the config.txt so that the kernel is booted
  directly without u-boot in between results in the full 4Gb being
  accessible:

      ubuntu at ubuntu:~$ free
                    total        used        free      shared  buff/cache   available
      Mem:        3884464      189852     3457504        3656      237108     3636004
      Swap:             0           0           0

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