Emanuele Ghidoli 0977448b45 common: memsize: add RAM size probe based on alias detection ...

Add probe_ram_size_by_alias() to detect RAM size by checking whether a
write to one address aliases to another address.

Compared to get_ram_size(), this function allows the caller to:
- limit probing to a small set of required accesses
- avoid touching reserved or already used memory regions
- handle non-linear alias patterns

On the iMX95 SoC, when used with LPDDR5, accesses beyond the end of an 8GB DDR
configuration do not alias to the expected linear wrap-around addresses.
Instead, the aliased addresses appear to follow a pattern related to the
DDRC bank and bank-group addresses mapping. Experimentally, the observed
pattern is:

Write        Read
y00000000 -> x0001c000
y00004000 -> x00018000
y00008000 -> x00014000
y0000c000 -> x00010000
y00010000 -> x0000c000
y00014000 -> x00008000
y00018000 -> x00004000
y0001c000 -> x00000000

This helper makes it possible to probe RAM size by explicitly specifying
the probed address and the expected alias address for each size check.

Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

2026-04-21 20:49:39 -03:00

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