netdev - Re: [PATCH net] net: phy: fix a signedness bug in genphy

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Message-ID: <ZHW7WPr1Ym2d8Hcc@shell.armlinux.org.uk>
Date: Tue, 30 May 2023 10:01:12 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Andrew Lunn <andrew@...n.ch>, Dan Carpenter <dan.carpenter@...aro.org>,
	Oleksij Rempel <linux@...pel-privat.de>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] net: phy: fix a signedness bug in genphy_loopback()

On Mon, May 29, 2023 at 09:58:02PM -0700, Jakub Kicinski wrote:
> On Fri, 26 May 2023 14:45:54 +0300 Dan Carpenter wrote:
> > The "val" variable is used to store error codes from phy_read() so
> > it needs to be signed for the error handling to work as expected.
> > 
> > Fixes: 014068dcb5b1 ("net: phy: genphy_loopback: add link speed configuration")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> 
> Is it going to be obvious to PHY-savvy folks that the val passed to
> phy_read_poll_timeout() must be an int? Is it a very common pattern?
> My outsider intuition is that since regs are 16b, u16 is reasonable,
> and more people may make the same mistake. Therefore we should try to
> fix phy_read_poll_timeout() instead to use a local variable like it
> does for __ret. 
> 
> Weaker version would be to add a compile time check to ensure val 
> is signed (assert(typeof(val)~0ULL < 0) or such?).
> 
> Opinions?

Yes, I think that would be a saner approach, since
phy_read_poll_timeout() returns the error value, rather than using
the variable passed in. Andrew?

-- 
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