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

[Dave Jones]

Figured it out; you're using the v2019.07-rpi4-wip branch while I based
the latest u-boot on the rpi4 branch (which is slightly later and
appears a bit more polished). After a bit of experimentation it turns
out the crucial difference is in the config, specifically in a comment
(which is why it took me a while to notice!):

    # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set

This line is missing from the rpi4 branch. Because ARCH_FIXUP_FDT_MEMORY
defaults to "y" this is enough to cause a call to
arch_fixup_memory_banks() in the packaged version of u-boot, which is
what causes the RAM to be limited to 1Gb (I haven't dug into the
mechanism why; for now I'm content to flip the config switch and have a
version that allows full access to the RAM, but I might have a look at
this if I get a bit of time next week).

Anyway, I'll get a new version of u-boot built and see if I can get
someone to sponsor it for release (might be too late, but it's not the
end of the world if it doesn't make it into the release; it'll be a
trivial update for users).

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

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

Status in u-boot package in Ubuntu:
  Confirmed

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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