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

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Message-ID: <20170601130900.GA22219@n2100.armlinux.org.uk>
Date:   Thu, 1 Jun 2017 14:09:00 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
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 Thu, Jun 01, 2017 at 03:05:27PM +0200, Andrew Lunn wrote:
> So you are saying a 10G PHY driver always needs to have a aneg_done
> callback, even if it just needs to call phygen_c45_aneg_done?
> 
> This seems a bit error prone. I can see somebody writing a 10G driver,
> leaving out aneg_done() and having the c22 version called. Is the read
> of MII_BMSR likely to return 0xffff, since the register does not
> exist? If so, genphy_aneg_done() is likely to always return
> BMSR_ANEGCOMPLETE.

Don't forget that the read will fail, so phy_read() will return a
negative number.  This practically (and I've tested it) means that
genphy_aneg_done() never indicates negotiation completion, and the
link never comes up.

> Seems like a trap waiting for somebody to fall into it. The additional
> code might be worth it to avoid placing this trap.

The "trap" means a non-functional driver, since the link doesn't
come up.

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