netdev - Re: [PATCH RFC net-next v2 03/12] net: mdio: mdiobus

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Date:   Mon, 9 Jan 2023 14:41:16 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Michael Walle <michael@...le.cc>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        Wei Fang <wei.fang@....com>,
        Shenwei Wang <shenwei.wang@....com>,
        Clark Wang <xiaoning.wang@....com>,
        NXP Linux Team <linux-imx@....com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, Andrew Lunn <andrew@...n.ch>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH RFC net-next v2 03/12] net: mdio: mdiobus_register:
 update validation test

On Mon, Jan 09, 2023 at 01:35:29PM +0100, Michael Walle wrote:
> Hi Russell,
> 
> Am 2023-01-03 23:19, schrieb Russell King (Oracle):
> > On Tue, Jan 03, 2023 at 11:21:08AM +0100, Michael Walle wrote:
> > > Am 2023-01-03 11:13, schrieb Russell King (Oracle):
> > > > On Wed, Dec 28, 2022 at 12:07:19AM +0100, Michael Walle wrote:
> > > > > +	if (!bus || !bus->name)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	/* An access method always needs both read and write operations */
> > > > > +	if ((bus->read && !bus->write) ||
> > > > > +	    (!bus->read && bus->write) ||
> > > > > +	    (bus->read_c45 && !bus->write_c45) ||
> > > > > +	    (!bus->read_c45 && bus->write_c45))
> > > >
> > > > I wonder whether the following would be even more readable:
> > > >
> > > > 	if (!bus->read != !bus->write || !bus->read_c45 != !bus->write_c45)
> > > 
> > > That's what Andrew had originally. But there was a comment from
> > > Sergey [1]
> > > which I agree with. I had a hard time wrapping my head around that,
> > > so I
> > > just listed all the possible bad cases.
> > 
> > The only reason I suggested it was because when looked at your code,
> > it also took several reads to work out what it was trying to do!
> > 
> > Would using !!bus->read != !!bus->write would help or make it worse,
> > !!ptr being the more normal way to convert something to a boolean?
> 
> IMHO that makes it even harder. But I doubt we will find an expression
> that will work for everyone. I'll go with your suggestion/Andrew's first
> version in the next iteration.

I think the double negation conveys the intention better than the simple
one, actually (maybe even xor instead of != ?). In terms of readability
I think I prefer the way the patch is written right now, but if you keep
the comment, the double negation should be pretty easy to swallow too.