netdev - Re: [PATCH v2 net] net: dsa: fix error code getting shifted with 4 in dsa_slave_get_sset

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Message-ID: <YJh/3unc5rM6oKvH@lunn.ch>
Date:   Mon, 10 May 2021 02:35:42 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH v2 net] net: dsa: fix error code getting shifted with 4
 in dsa_slave_get_sset_count

On Sun, May 09, 2021 at 10:33:38PM +0300, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> DSA implements a bunch of 'standardized' ethtool statistics counters,
> namely tx_packets, tx_bytes, rx_packets, rx_bytes. So whatever the
> hardware driver returns in .get_sset_count(), we need to add 4 to that.
> 
> That is ok, except that .get_sset_count() can return a negative error
> code, for example:
> 
> b53_get_sset_count
> -> phy_ethtool_get_sset_count
>    -> return -EIO
> 
> -EIO is -5, and with 4 added to it, it becomes -1, aka -EPERM. One can
> imagine that certain error codes may even become positive, although
> based on code inspection I did not see instances of that.
> 
> Check the error code first, if it is negative return it as-is.
> 
> Based on a similar patch for dsa_master_get_strings from Dan Carpenter:
> https://patchwork.kernel.org/project/netdevbpf/patch/YJaSe3RPgn7gKxZv@mwanda/
> 
> Fixes: 91da11f870f0 ("net: Distributed Switch Architecture protocol support")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew