[PATCH] lmb: Reinstate access to memory above ram_top

[Simon Glass]

Hi Marek, Mark,

On Tue, 27 Jan 2026 at 16:49, Marek Vasut
<marek.vasut+renesas at mailbox.org> wrote:
>
> Revert commit eb052cbb896f ("lmb: add and reserve memory above ram_top")
> and commit 1a48b0be93d4 ("lmb: prohibit allocations above ram_top even from
> same bank"). These are based on incorrect premise of the first commit, that
> "U-Boot does not use memory above ram_top". While U-Boot itself indeed does
> not and should not use memory above ram_top, user can perfectly well use
> that memory from the U-Boot shell, for example to load content in there.
>
> Currently, attempt to use that memory to load large image using TFTP ends
> with "TFTP error: trying to overwrite reserved memory...". With this change
> in place, the memory can be used again.
>
> Fixes: eb052cbb896f ("lmb: add and reserve memory above ram_top")
> Fixes: 1a48b0be93d4 ("lmb: prohibit allocations above ram_top even from same bank")
> Reported-by: Yuya Hamamachi <yuya.hamamachi.sx at renesas.com>
> Signed-off-by: Marek Vasut <marek.vasut+renesas at mailbox.org>
> ---
> Cc: Andrew Goodbody <andrew.goodbody at linaro.org>
> Cc: Casey Connolly <casey.connolly at linaro.org>
> Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
> Cc: Holger Brunck <holger.brunck at hitachienergy.com>
> Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> Cc: Jonas Karlman <jonas at kwiboo.se>,
> Cc: Mark Kettenis <kettenis at openbsd.org>
> Cc: Sam Protsenko <semen.protsenko at linaro.org>
> Cc: Sughosh Ganu <sughosh.ganu at linaro.org>
> Cc: Tom Rini <trini at konsulko.com>
> Cc: u-boot at lists.denx.de
> ---
>  lib/lmb.c | 17 +----------------
>  1 file changed, 1 insertion(+), 16 deletions(-)
>
> diff --git a/lib/lmb.c b/lib/lmb.c
> index e2d9fe86c14..8f12c6ad8e5 100644
> --- a/lib/lmb.c
> +++ b/lib/lmb.c
> @@ -611,7 +611,6 @@ static __maybe_unused void lmb_reserve_common_spl(void)
>  static void lmb_add_memory(void)
>  {
>         int i;
> -       phys_addr_t bank_end;
>         phys_size_t size;
>         u64 ram_top = gd->ram_top;
>         struct bd_info *bd = gd->bd;
> @@ -625,23 +624,9 @@ static void lmb_add_memory(void)
>
>         for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {
>                 size = bd->bi_dram[i].size;
> -               bank_end = bd->bi_dram[i].start + size;
>
> -               if (size) {
> +               if (size)
>                         lmb_add(bd->bi_dram[i].start, size);
> -
> -                       /*
> -                        * Reserve memory above ram_top as
> -                        * no-overwrite so that it cannot be
> -                        * allocated
> -                        */
> -                       if (bd->bi_dram[i].start >= ram_top)
> -                               lmb_reserve(bd->bi_dram[i].start, size,
> -                                           LMB_NOOVERWRITE);
> -                       else if (bank_end > ram_top)
> -                               lmb_reserve(ram_top, bank_end - ram_top,
> -                                           LMB_NOOVERWRITE);
> -               }
>         }
>  }
>
> --
> 2.51.0
>

A bit late, but this seems to break rpi5 for me - the board in my lab
has only 2G of memory.

Has anyone else noticed this? I can send a patch if not.

Regards,
Simon