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 16:48:37 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Marek Behún <marek.behun@....cz>
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, Aug 12, 2020 at 05:37:16PM +0200, Marek Behún wrote:
> 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?

Well, I have other questions about it.  Why are you doing it in
the power_up function?  Do you find that the MACTYPE field is
lost when clearing the power down bit?  From what I read, it should
only change on hardware reset, and we don't hardware reset when we
come out of power down - only software reset.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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