Merge branch 'phylink-pcs-validation'

Merge branch 'phylink-pcs-validation'

Russell King says:

====================
net: phylink: add PCS validation

This series allows phylink to include the PCS in its validation step.
There are two reasons to make this change:

1. Some of the network drivers that are making use of the split PCS
   support are already manually calling into their PCS drivers to
   perform validation. E.g. stmmac with xpcs.

2. Logically, some network drivers such as mvneta and mvpp2, the
   restriction we impose in the validate() callback is a property of
   the "PCS" block that we provide rather than the MAC.

This series:

1. Gives phylink a mechanism to query the MAC driver which PCS is
   wishes to use for the PHY interface mode. This is necessary to allow
   the PCS to be involved in the validation step without making changes
   to the configuration.

2. Provide a pcs_validate() method that PCS can implement. This follows
   a similar model to the MAC's validate() callback, but with some minor
   differences due to observations from the various implementations.
   E.g. returning an error code for not-supported and the way the
   advertising bitmap is masked.

3. Convert mvpp2 and mvneta to this as examples of its use. Further
   Conversions are in the pipeline, including for stmmac+xpcs, as well
   as some DSA drivers. Note that DSA conversion to this is conditional
   upon all DSA drivers populating their supported_interfaces bitmap,
   since this is required before mac_select_pcs() can be used.

Existing drivers that set a PCS in mac_prepare() or mac_config(), or
shortly after phylink_create() will continue to work. However, it should
be noted that mac_select_pcs() will be called during phylink_create(),
and thus any PCS returned by mac_select_pcs() must be available by this
time - or we drop the check in phylink_create().

v2: fix kerneldoc typo in patch 1.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>