netdev - Re: [PATCH RFC russell-king 3/4] net: phy: marvell10g: change MACTYPE according to phydev->interface

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Date:   Wed, 12 Aug 2020 17:37:16 +0200
From:   Marek Behún <marek.behun@....cz>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Baruch Siach <baruch@...s.co.il>,
        Chris Healy <cphealy@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC russell-king 3/4] net: phy: marvell10g: change
 MACTYPE according to phydev->interface

On Wed, 12 Aug 2020 16:00:54 +0100
Russell King - ARM Linux admin <linux@...linux.org.uk> wrote:

> On Wed, Aug 12, 2020 at 04:44:31PM +0200, Marek Behún wrote:
> > There is another problem though: I think the PHY driver, when
> > deciding whether to set MACTYPE from the XFI with rate matching
> > mode to the 10GBASE-R/5GBASE-R/2500BASE-X/SGMII with AN mode,
> > should check which modes the underlying MAC support.  
> 
> I'm aware of that problem.  I have some experimental patches which add
> PHY interface mode bitmaps to the MAC, PHY, and SFP module parsing
> functions.  I have stumbled on some problems though - it's going to be
> another API change (and people are already whinging about the phylink
> API changing "too quickly", were too quickly seems to be defined as
> once in three years), and in some cases, DSA, it's extremely hard to
> work out how to properly set such a bitmap due to DSA's layered
> approach.
> 

If by your experimental patches you mean
  net: mvneta: fill in phy interface mode bitmap
  net: mvpp2: fill in phy interface mode bitmap
found here
  http://git.arm.linux.org.uk/cgit/linux-arm.git/log/?h=clearfog
I am currently working on top of them.

> Having bitmaps means that we can take the union of what the MAC and
> PHY supports, and decide which MACTYPE setting would be most suitable.
> However, to do that we're into also changing phylib's interfaces as
> well.
> 
> > driver to phylink in the call to phylink_create. But there is no way
> > for the PHY driver to get this information from phylink currently,
> > and even if phylink exposed a function to return the config member
> > of struct phylink, the problem is that at the time when
> > mv3310_power_up is called, the phydev->phylink is not yet set (this
> > is done in phylink_bringup_phy, and mv3310_power_up is called
> > sometime in the phylink_attach_phy).  
> 
> We _really_ do not want phylib calling back into phylink functions.
> That would tie phylink functionality into phylib and cause problems
> when phylink is not being used.
> 
> I would prefer phylib to be passed "the MAC can use these interface
> types, and would prefer to use this interface type" and have the
> phylib layer (along with the phylib driver) make the decision about
> which mode should be used.  That also means that non-phylink MACs
> can also use it.
> 

I may try to propose something, but in the meantime do you think the
current version of the patch
  net: phy: marvell10g: change MACTYPE according to phydev->interface
is acceptable?

Marek