net: l2: ieee802154: document non-standard channel page selection

The IEEE 802.15.4 standard does not specify a "Sub-GHz" option.
Therefore this option will be deprecated in the foreseeable future.

Rationale: Selecting PHYs and frequency bands is abstracted by the
concept of channel pages (see IEEE 802.15.4-2020, 10.1.3).

Radio drivers may expose additional configuration options that
specify the low level frequency band, operating mode and other
PHY-specific parameters. Such parameters should be exposed on a driver
instance level, e.g. via devicetree or as runtime options of the driver.
PHY-specific attributes derived from driver settings (e.g. available
channels) can then be announced to L2 w/o the user having to be aware of
any implementation details of the specific PHY.

Future changes will introduce the necessary infrastructure to define
channel pages and other PHY-specific configuration options to
replace this option. New drivers should therefore not rely on this
option.

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>

subsys/net/l2/ieee802154/Kconfig

@@ -14,6 +14,15 @@ config NET_L2_IEEE802154_MGMT
 	select NET_MGMT
 	select NET_MGMT_EVENT
 
+# TODO: Selecting PHYs and frequency bands is abstracted by the concept
+#       of channel pages in recent versions of the standard (see
+#       IEEE 802.15.4-2020, 10.1.3).
+#       This option will be replaced by configuration options on driver
+#       instance level that allow selection of a channel page as well
+#       as other PHY-specific configuration options (frequency bands,
+#       operating modes, etc.).
+#       New and existing drivers should not introduce additional
+#       references to this option.
 config NET_L2_IEEE802154_SUB_GHZ
 	bool
 	help