netdev - Re: [PATCH 2/5] net: phy: hook up clause 45 autonegotiation restart

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Message-ID: <20170602134632.GI12261@lunn.ch>
Date:   Fri, 2 Jun 2017 15:46:32 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/5] net: phy: hook up clause 45 autonegotiation restart

On Fri, Jun 02, 2017 at 01:43:39PM +0100, Russell King - ARM Linux wrote:
> On Thu, Jun 01, 2017 at 10:16:17AM -0700, Florian Fainelli wrote:
> > On 06/01/2017 09:24 AM, Russell King - ARM Linux wrote:
> > > Checking 802.3-2015, in "22.2.4 Management functions", the first
> > > sentence requires all PHYs that respond to Clause 22 cycles to
> > > implement BMCR and BMSR.  However, my statement about unimplemented
> > > registers returning zero seems to be a C45 thing, not a C22 thing,
> > > according to the C22 PICS and "45.2 MDIO Interface Registers"
> > > 
> > > However, digging a bit further, "22.2.4.2.10 Auto-Negotiation complete"
> > > states that bit 5 shall be zero if aneg has not completed or if aneg is
> > > unimplemented.
> > > 
> > 
> > So how about we are more defensive than that and if we are presented
> > with a C45 PHY driver that does not have an aneg_done() function pointer
> > set we return an error/warning during driver registration?
> 
> We don't mark drivers as being C22 or C45, we rely on them matching
> the IDs and/or the probe function making that decision, so it's a
> tad difficult to make that decision at driver registration time.
> 
> We could reject an attempt to probe a C45 phy with a driver that
> does not provide an aneg_done() pointer.

Just an idea.

We could make phy_read/phy_write look to see if the is_c45 flag is
set. If so, return -EINVAL if the register being accessed does not
have MII_ADDR_C45.

That should catch all these sort of problems.

     Andrew