Re: [RFC net-next 2/5] net: phylink: add separate pcs operations structure

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Tue, Mar 17, 2020 at 05:38:02PM +0100, Andrew Lunn wrote:
> On Tue, Mar 17, 2020 at 02:52:51PM +0000, Russell King wrote:
> > *NOT FOR MERGING*
> > 
> > Add a separate set of PCS operations, which MAC drivers can use to
> > couple phylink with their associated MAC PCS layer.  The PCS
> > operations include:
> > 
> > - pcs_get_state() - reads the link up/down, resolved speed, duplex
> >    and pause from the PCS.
> > - pcs_config() - configures the PCS for the specified mode, PHY
> >    interface type, and setting the advertisement.
> > - pcs_an_restart() - restarts 802.3 in-band negotiation with the
> >    link partner
> > - pcs_link_up() - informs the PCS that link has come up, and the
> >    parameters of the link. Link parameters are used to program the
> >    PCS for fixed speed and non-inband modes.
> 
> Hi Russell
> 
> This API makes sense. But it seems quite common to have multiple
> PCS's. Rather than have MAC drivers implement their own mux, i wonder
> if there should be core support? Or at least a library to help the
> implementation?

When each PCS has different characteristics, and may not even be
available to be probed (because the hardware holds them in reset,
so they don't even respond to MDIO cycles) that becomes very
difficult.

That is the situation with LX2160A - when in 1G mode, the 10G C45
PCS does not respond.  Already tested that.

So, determining when to switch can't be known by generic code.

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