Re: [PATCH V2 net-next 2/5] net: Introduce a new MII time stamping interface.

On Sun, Oct 07, 2018 at 01:59:06PM -0700, Richard Cochran wrote:

On Sun, Oct 07, 2018 at 09:54:00PM +0200, Andrew Lunn wrote:

quoted

Sure, but things have moved on since then.

If you have a specific suggestion on how to better implement this,
please tell us what it is.
  

quoted

I can think of three obvious use cases where this does not work:

1) phylink, not phdev. We have been pushing some MAC drivers towards
phylink, especially those which support >1Gbp.

If a phylink device appears that wants time stamping, can't we add the
call to register_mii_timestamper()?

Hi Richard

The problem is you depend on skbuf->dev->phydev. phydev will be NULL.
net_device does not currently have a phylink member. Even if it did,
you end up add more and more tests looking every place a
mii_timestamper could be placed.
  

quoted

2) When an SFP is connected to the MAC, not a copper PHY. The class of
device you are adding a driver for will work just as well for an SFP
as for a copper PHY. The SERDES interface remains the same,
independent of if a copper PHY is used, or a SFP. But an SFP does not
have an instance of a phydv.

Well, as I said before in v1, CONFIG_NETWORK_PHY_TIMESTAMPING depends
on phylib, plain and simple, and expanding beyond phylib is not within
the scope of the this series.

True. But we also should be forward looking, to make sure we are not
heading into a dead end.

I'm currently thinking register_mii_timestamper() should take a netdev
argument, and the net_device structure should gain a struct
mii_timestamper.

But we have to look at the lifetime problems. A phydev does not know
what netdev it is associated to until phy_connect() is called. It is
at that point you can call register_mii_timestamper().

   Andrew