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

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Date:   Thu, 11 Jan 2018 16:54:57 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     David Miller <davem@...emloft.net>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: phy: Fix phy_modify() semantic difference fallout

On Thu, Jan 11, 2018 at 4:53 PM, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> On Thu, Jan 11, 2018 at 10:48:35AM -0500, David Miller wrote:
>> From: Geert Uytterhoeven <geert+renesas@...der.be>
>> Date: Tue,  9 Jan 2018 12:11:21 +0100
>>
>> > 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?
>>
>> I really want a resolution to this quickly, this broke lots of stuff
>> for people.
>>
>> __phy_modify() wants to return multiple values, so it should be coded
>> up to do so explicitly rather than trying to encode two values from
>> overlapping value spaces in one return value.
>>
>> That means the original value should be returned by-reference.  And
>> this will make the error/no-error return value unambiguous.
>>
>> int __phy_modify(struct phy_device *phydev, u32 regnum, u16 mask, u16 set,
>>                u16 *orig_val);
>
> I'm sorry I have no time to work on this right now due to the meltdown
> and spectre stuff that hit last week.  If you need to do something,
> please revert both the mvneta series and the series containing this
> patch.

I'll have a look into it...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds