net: macb: Fix several edge cases in validate

There were several cases where validate() would return bogus supported
modes with unusual combinations of interfaces and capabilities. For
example, if state->interface was 10GBASER and the macb had HIGH_SPEED
and PCS but not GIGABIT MODE, then 10/100 modes would be set anyway. In
another case, SGMII could be enabled even if the mac was not a GEM
(despite this being checked for later on in mac_config()). These
inconsistencies make it difficult to refactor this function cleanly.

There is still the open question of what exactly the requirements for
SGMII and 10GBASER are, and what SGMII actually supports. If someone
from Cadence (or anyone else with access to the GEM/MACB datasheet)
could comment on this, it would be greatly appreciated. In particular,
what is supported by Cadence vs. vendor extension/limitation?

To address this, the current logic is split into three parts. First, we
determine what we support, then we eliminate unsupported interfaces, and
finally we set the appropriate link modes. There is still some cruft
related to NA, but this can be removed in a future patch.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Parshuram Thombare <pthombar@cadence.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20211112190400.1937855-1-sean.anderson@seco.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>