If the DTB for a device with an RZ/A2 SoC lacks a device node for the
BSID register, the ID validation code falls back to using a register at
address 0x0, which leads to undefined behavior (e.g. reading back a
random value).
This could be fixed by letting fam_rza2.reg point to the actual BSID
register. However, the hardcoded fallbacks were meant for backwards
compatibility with old DTBs only, not for new SoCs. Hence fix this by
validating renesas_family.reg before using it.
Fixes: 175f435f44 ("soc: renesas: identify RZ/A2")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20191016143306.28995-1-geert+renesas@glider.be
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