doc: phy: Document typical order of API calls

Document the typical order of API calls to used by new drivers and
controllers. Many existing controllers follow this order, but some do
not. This is especially true for controllers designed to work with one
particular PHY driver, which may not need a call to (for example)
phy_init.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20221018175841.1906611-1-sean.anderson@seco.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/driver-api/phy/phy.rst

@@ -94,7 +94,8 @@ Inorder to dereference the private data (in phy_ops), the phy provider driver
 can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
 phy_ops to get back the private data.
 
-4. Getting a reference to the PHY
+Getting a reference to the PHY
+==============================
 
 Before the controller can make use of the PHY, it has to get a reference to
 it. This framework provides the following APIs to get a reference to the PHY.
@@ -130,6 +131,28 @@ the phy_init() and phy_exit() calls, and phy_power_on() and
 phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
 phy is useful in devices for handling optional phy devices.
 
+Order of API calls
+==================
+
+The general order of calls should be::
+
+    [devm_][of_]phy_get()
+    phy_init()
+    phy_power_on()
+    [phy_set_mode[_ext]()]
+    ...
+    phy_power_off()
+    phy_exit()
+    [[of_]phy_put()]
+
+Some PHY drivers may not implement :c:func:`phy_init` or :c:func:`phy_power_on`,
+but controllers should always call these functions to be compatible with other
+PHYs. Some PHYs may require :c:func:`phy_set_mode <phy_set_mode_ext>`, while
+others may use a default mode (typically configured via devicetree or other
+firmware). For compatibility, you should always call this function if you know
+what mode you will be using. Generally, this function should be called after
+:c:func:`phy_power_on`, although some PHY drivers may allow it at any time.
+
 Releasing a reference to the PHY
 ================================