Replace rtpcs_838x_sds_set_mode()'s inline shift/mask arithmetic with
a regmap_field computed and allocated at probe time. The field layout
is regular (5-bit per SerDes, reverse-packed in SDS_MODE_SEL), so the
position can be derived arithmetically from the SerDes ID rather than
declared in a table.
The function keeps its wrapper role because SerDes 4 and 5 have a
second companion register (INT_MODE_CTRL) with its own per-mode value
encoding. Since RTL838x is the only variant with this quirk and the
register is written from only one call site, it is kept inline rather
than abstracted into its own config table.
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23040
Signed-off-by: Robert Marko <robimarko@gmail.com>
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