[REGRESSION] lmb: add and reserve memory above ram_top

[Sam Protsenko]

On Thu, Dec 5, 2024 at 11:23 PM Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
>

[snip]

> >     ERROR: reserving fdt memory region failed (addr=bab00000
> > size=5500000 flags=2)
> >     ERROR: reserving fdt memory region failed (addr=f0000000
> > size=200000 flags=4)
> >
> > It looks like all mentioned error messages are harmless, in a way that
> > I'm still able to boot Linux, and U-Boot reserved areas still seem to
> > exist in 'bdinfo'. But seeing error messages like that is definitely a
> > nuisance by itself, and might be an indicator of some actual issues.
> > Do you have any remedy for that by chance? Please let me know if you
> > need more debug input from my side.
>
> This seems to be happening because the board is trying to reserve
> memory above ram_top with no-map or no-overwrite attributes. To
> confirm, you can print the value of ram_top in setup_dest_addr().
>
> -sughosh
>

Thanks for your input, Sughosh! I did a bit of further analysis, and
found the mentioned error message is happening on 3 different
occasions. All 3 of them are caused by the recent LMB patches merged
in U-Boot/master. They are all probably harmless, but a bit
misleading. Also, I'm not sure whether they are actually *causing*
those errors, or just revealing some already existing issues.
Specifically those 3 occurrences are:

1. The one reported in this thread. The root cause, like you
suggested, is the board trying to reserve the memory above ram_top.
It's actually happening in lmb_init(). Details:

  - The 'memory' node from my dts:

        memory at 80000000 {
            device_type = "memory";
            reg = <0x0 0x80000000 0x3ab00000>,
                  <0x0 0xc0000000 0x40000000>,
                  <0x8 0x80000000 0x80000000>;
        };

  - Reserved memory chunk: (addr=f0000000 size=200000 flags=4).
    That's 'ramoops' chunk from the 'reserved-memory' node in my dts.
  - ram_top (as seen in lmb_init) = 0xbab0_0000.
    That's because my board's dram_init() calls the
fdtdec_setup_mem_size_base(), which only takes the first cell from the
'memory' node.
    Which is 0x8000_0000 ... 0xbab0_0000.
  - So the reserved memory is above ram_top, as you suggested.
  - Not sure how to properly fix it though. Maybe I need to "teach"
U-Boot to use all 3 chunks from my 'memory' node somehow?
  - I was able to work-around it by reworking the 'memory' node in my
device tree as described in my first message in this thread:

        memory at 80000000 {
            device_type = "memory";
            reg = <0x0 0x80000000 0x80000000>,
                  <0x8 0x80000000 0x80000000>;
        };

2. When booting Linux with 'booti' command, there happens the repeated
attempt to reserve all 'reserved-memory' chunks, which were already
reserved during the board init, which also leads to similar error
messages. I addressed that one (hopefully properly) in my series [1].
Please take a look. That one is caused by a combination of these two
commits:

  - 1d9aa4a283da ("lmb: Fix the allocation of overlapping memory areas
with !LMB_NONE")
  - 827dee587b75 ("fdt: lmb: add reserved regions as no-overwrite")

3. I noticed another similar error message when running sandbox U-Boot on my PC:

        $ make sandbox_defconfig
        $ make -j32
        $ ./u-boot -D
        ...
        ERROR: reserving fdt memory region failed (addr=fffe000
size=2000 flags=2)

  Can you please check that one on your U-Boot/master? I was able to
narrow it down to commit 6534d26ee9a5 ("lmb: do away with
arch_lmb_reserve()"), if that helps.

Thanks!

[1] https://lists.denx.de/pipermail/u-boot/2024-December/574308.html