Re: [PATCH net-next v2 0/2] Enable 2.5Gbps speed for stmmac

The limitation is not on the MAC, PCS or the PHY. For Intel mgbe, the
overclocking of 2.5 times clock rate to support 2.5G is only able to be
configured in the BIOS during boot time. Kernel driver has no access to 
modify the clock rate for 1Gbps/2.5G mode. The way to determined the 
current 1G/2.5G mode is by reading a dedicated adhoc register through mdio bus.
In short, after the system boot up, it is either in 1G mode or 2.5G mode 
which not able to be changed on the fly. 

Right. It would of been a lot easier if this was in the commit message
from the beginning. Please ensure the next version does say this.

Since the stmmac MAC can pair with any PCS and PHY, I still prefer that we tie
this platform specific limitation with the of MAC. As stmmac does handle platform
specific config/limitation. 

So yes, this needs to be somewhere in the intel specific stmmac code,
with a nice comment explaining what is going on.

What PHY are you using? The Aquantia/Marvell multi-gige phy can do
rate adaptation. So you could fix the MAC-PHY link to 2500BaseX, and
let the PHY internally handle the different line speeds.

    Andrew