netdev - Re: [PATCH] net: phy: Fix phy_modify() semantic difference fallout

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Message-ID: <20180109142248.GG17719@n2100.armlinux.org.uk>
Date:   Tue, 9 Jan 2018 14:22:48 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        "David S . Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: Fix phy_modify() semantic difference fallout

On Tue, Jan 09, 2018 at 03:10:08PM +0100, Andrew Lunn wrote:
> On Tue, Jan 09, 2018 at 12:11:21PM +0100, Geert Uytterhoeven wrote:
> > In case of success, the return values of (__)phy_write() and
> > (__)phy_modify() are not compatible: (__)phy_write() returns 0, while
> > (__)phy_modify() returns the old PHY register value.
> > 
> > Apparently this change was catered for in drivers/net/phy/marvell.c, but
> > not in other source files.
> > 
> > Hence genphy_restart_aneg() now returns 4416 instead zero, which is
> > considered an error:
> > 
> >     ravb e6800000.ethernet eth0: failed to connect PHY
> >     IP-Config: Failed to open eth0
> >     IP-Config: No network devices available
> > 
> > Fix this by converting positive values to zero in all callers of
> > phy_modify().
> > 
> > Fixes: fea23fb591cce995 ("net: phy: convert read-modify-write to phy_modify()")
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > ---
> > Alternatively, __phy_modify() could be changed to follow __phy_write()
> > semantics?
> 
> Hi Geert, Russell
> 
> I took a quick look at the uses of phy_modify(). I don't see any uses
> of the return code other than as an error indicator. So having it
> return 0 on success seems like a better fix.

I'd like to avoid that, because I don't want to have yet another
accessor that needs to be used for advertisment modification (where
we need to know if we changed any bits.)

That's why this accessor returns the old value.

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