[PATCH v1] common: memsize: fix occasionally failing alias probing

[Simon Glass]

On 2026-04-29T10:03:56, Emanuele Ghidoli <ghidoliemanuele at gmail.com> wrote:
> common: memsize: fix occasionally failing alias probing
>
> probe_ram_size_by_alias() detects whether a probe address still aliases
> a lower address by writing through one address and reading through the
> other.
>
> On i.MX95 this occasionally reported a false non-alias when the alias
> read happened immediately after the write.
>
> A memory barrier alone, mb(), was tested but did not make the failure go
> away. This suggests that ordering the CPU accesses is not sufficient for
> this probe, likely because the issue is in the path to the memory
> controller rather than in the core itself.
>
> Read the written address back before checking the alias address. This
> appears to force the write to become observable at the probe address
> before using the alias read to decide whether the tested address range
> exists.
>
> If the readback does not match the written pattern, restore the saved
> value and continue with the next check. This keeps the probe robust for
> addresses that do not reliably retain the test pattern.
>
> Fixes: 0977448b45e2 ("common: memsize: add RAM size probe based on alias detection")
> Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli at toradex.com>
>
> common/memsize.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)

Reviewed-by: Simon Glass <sjg at chromium.org>