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From:   "Voon, Weifeng" <weifeng.voon@intel.com>
To:     Andrew Lunn <andrew@lunn.ch>
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Subject: RE: [PATCH net-next v2 0/2] Enable 2.5Gbps speed for stmmac
Thread-Topic: [PATCH net-next v2 0/2] Enable 2.5Gbps speed for stmmac
Thread-Index: AQHXKg/Os9IaztXPaUy24X7Nc4wW6qql5igAgAAULACAAANOgIABLtjggAC//4CAAGteEA==
Date:   Wed, 7 Apr 2021 03:02:21 +0000
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> > 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.
>=20
> 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.
>=20
> > 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.
>=20
> So yes, this needs to be somewhere in the intel specific stmmac code,
> with a nice comment explaining what is going on.
>=20
> 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.
>=20
Intel mgbe is flexible to pair with any PHY. Only Aquantia/Marvell
multi-gige PHY can do rate adaption right? Hence, we still need to take=20
care of others PHYs.

Thanks for all the comments, will include them in v3.=20

Weifeng