netdev - Re: [PATCH] net: usb: dm9601: fix wrong return value in dm9601_mdio

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Message-ID: <20240227160918.GB277116@kernel.org>
Date: Tue, 27 Feb 2024 16:09:18 +0000
From: Simon Horman <horms@...nel.org>
To: Javier Carrasco <javier.carrasco.cruz@...il.com>
Cc: Peter Korsgaard <peter@...sgaard.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: usb: dm9601: fix wrong return value in
 dm9601_mdio_read

On Sun, Feb 25, 2024 at 12:20:06AM +0100, Javier Carrasco wrote:
> The MII code does not check the return value of mdio_read (among
> others), and therefore no error code should be sent. A previous fix to
> the use of an uninitialized variable propagates negative error codes,
> that might lead to wrong operations by the MII library.
> 
> An example of such issues is the use of mii_nway_restart by the dm9601
> driver. The mii_nway_restart function does not check the value returned
> by mdio_read, which in this case might be a negative number which could
> contain the exact bit the function checks (BMCR_ANENABLE = 0x1000).
> 
> Return zero in case of error, as it is common practice in users of
> mdio_read to avoid wrong uses of the return value.
> 
> Fixes: 8f8abb863fa5 ("net: usb: dm9601: fix uninitialized variable use in dm9601_mdio_read")
> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>

I guess it would be nice if error values could be used,
but as you have described, that does not seem to be the case here.

Reviewed-by: Simon Horman <horms@...nel.org>