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

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Message-ID: <fb553ce5-c533-44a2-a134-fbb552f247bb@kili.mountain>
Date: Tue, 30 May 2023 17:40:11 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Jakub Kicinski <kuba@...nel.org>, Russell King <linux@...linux.org.uk>,
	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 Tue, May 30, 2023 at 02:39:53PM +0200, Andrew Lunn wrote:
> 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.
> 
> It is common to get this wrong in general with PHY drivers. Dan
> regularly posts fixes like this soon after a PHY driver patch it
> merged. I really wish we could somehow get the compiler to warn when
> the result from phy_read() is stored into a unsigned type. It would
> save Dan a lot of work.

I don't see these as much as I used.  It's maybe once per month.  I'm
not sure why, maybe kbuild emails everyone before I see it?  GCC will
warn about this with -Wtype-limits.  Clang will also trigger a warning.

The Smatch check for this had a bug where it only warned about if
(x < 0) { if x was u32 or larger.  I fixed that bug which is why I was
looking at this code.  I will push the fix for that in a couple days.

regards,
dan carpenter