netdev - Re: [PATCH net-next RFC V1 5/5] net: mdio: Add a driver for InES time stamping IP core.

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Date:   Sun, 25 Mar 2018 15:10:04 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        David Miller <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next RFC V1 5/5] net: mdio: Add a driver for InES
 time stamping IP core.

On Sun, Mar 25, 2018 at 05:59:37PM +0200, Andrew Lunn wrote:
> > > 3) How do you limit the MAC/PHY to what the PTP device can do.
> > 
> > Hm, I don't think this is important.
> 
> So you are happy that the PTP device will cause the MC/PHY link to
> break down when it is asked to do something it cannot do?

No, but I do expect the system designer to use common sense.  No need
to over engineer this now just to catch hypothetical future problems.

> > Right, so phylib can operate on phydev->attached_dev->mdiots;
> 
> So first off, it is not an MDIO device.

...

> To keep lifecycle issues simple, i would also keep it in phydev, not
> netdev.
> 
> mdiots as a name is completely wrong. It is not an MDIO device.

I am well aware of what terms MDIO and MII represent, but our current
code is hopelessly confused.  Case in point:

	static inline struct mii_bus *mdiobus_alloc(void);

The kernel's 'struct mii_bus' is really only about MDIO and not about
the rest of MII.  Clearly MII time stamping devices belong on the MII
bus, so that is where I put them.

Or maybe mii_bus should first be renamed to mdio_bus?  That you pave
the way for introducing a representation of the MII bus.

> in the future some devices will be MDIO, or I2C, or SPI. Just call it
> ptpdev. This ptpdev needs to be control bus agnostic. You need a
> ptpdev core API exposing functions like ptpdev_hwtstamp,
> ptpdev_rxtstamp, ptpdev_txtstamp, ptpdev_link_change, which take a
> ptpdev.

Well, this name is not ideal, since time stamping devices in general
can time stamp any frame, not just PTP frames.

> You can then clean up the code in timestamping.c. Code like:
> 
>         phydev = skb->dev->phydev;
>         if (likely(phydev->drv->txtstamp)) {
>                 clone = skb_clone_sk(skb);
>                 if (!clone)
>                         return;
>                 phydev->drv->txtstamp(phydev, clone, type);
>         }
> 
> violates the layering, and the locking looks broken.

Are you sure the locking is broken?  If so, how?

(This code path has been reviewed more than once.)

Can you please explain the layering and how this code breaks it?

(This code goes back to 2.6.36 and perhaps predates the layers that
were added later on.)

Thanks,
Richard