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

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Date: Mon, 29 May 2023 21:58:02 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Andrew Lunn <andrew@...n.ch>, Russell King <linux@...linux.org.uk>
Cc: 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 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?