[PATCH RFC] Providing a helper for PCS inband negotiation

[Russell King (Oracle)]

On Mon, May 15, 2023 at 10:56:16PM +0300, Vladimir Oltean wrote:
> Hello,
> 
> On Mon, May 15, 2023 at 01:22:50PM +0100, Russell King (Oracle) wrote:
> > 1. Should 10GBASE-KR be included in the SGMII et.al. case in the code?
> >    Any other interface modes that should be there? Obviously,
> >    PHYLINK_PCS_NEG_NONE is not correct for 10GBASE-KR since it does use
> >    inband AN. Does it make sense for the user to disable inband AN for
> >    10GBASE-KR? If so, maybe it should be under the 1000base-X case.
> 
> What physical process (reference to IEEE 802.3 clause is fine) would be
> controlled by the phylink_pcs_neg_mode() function for the so-called
> 10GBASE-KR phy-mode?

Clause 73.1:

"While implementation of Auto-Negotiation is mandatory for Backplane
Ethernet PHY s, the use of Auto-Negotiation is optional."

"The Auto-Negotiation function allows the devices to switch between
the various operational modes in an orderly fashion, permits
management to disable or enable the Auto-Negotiation function, and
allows management to select a specific operational mode."

"The Auto-Negotiation function also provides a parallel detection
function to allow Backplane Ethernet devices to connect to other
Backplane Ethernet devices that have Auto-Negotiation disabled and
interoperate with legacy devices that do not support Clause 73
Auto-Negotiation."

So, my reading of these statements is that the _user_ should be
able to control via ethtool whether Clause 73 negotiation is
performed on a 10GBASE-KR (or any other backplane link that
uses clause 73 negotiation.) Having extracted that from 802.3,
I now believe it should be treated the same as 1000BASE-X, and
the Autoneg bit in ethtool should determine whether Clause 73
negotiation is used for 10GBASE-KR (and any other Clause 73
using protocol.)

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