linux-kernel - Re: [PATCH net-next 07/15] net: dsa: mt7530: do not run mt7530_setup

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Message-ID: <90fde560-054e-4188-b15c-df2e082d3e33@moroto.mountain>
Date:   Thu, 7 Dec 2023 09:51:07 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Arınç ÜNAL <arinc.unal@...nc9.com>
Cc:     Simon Horman <horms@...nel.org>,
        Daniel Golle <daniel@...rotopia.org>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Bartel Eerdekens <bartel.eerdekens@...stell8.be>,
        mithat.guner@...ont.com, erkin.bozoglu@...ont.com
Subject: Re: [PATCH net-next 07/15] net: dsa: mt7530: do not run
 mt7530_setup_port5() if port 5 is disabled

On Sat, Dec 02, 2023 at 11:45:42AM +0300, Arınç ÜNAL wrote:
> 
> I'm not sure why it doesn't catch that for mt7530_setup_port5() to run
> here, priv->p5_intf_sel must be either P5_INTF_SEL_PHY_P0 or
> P5_INTF_SEL_PHY_P4. And for that to happen, the interface variable will be
> initialised.
> 
> for_each_child_of_node(dn, mac_np) {
> 	if (!of_device_is_compatible(mac_np,
> 				     "mediatek,eth-mac"))
> 		continue;
> 
> 	ret = of_property_read_u32(mac_np, "reg", &id);
> 	if (ret < 0 || id != 1)
> 		continue;
> 
> 	phy_node = of_parse_phandle(mac_np, "phy-handle", 0);
> 	if (!phy_node)
> 		continue;
> 
> 	if (phy_node->parent == priv->dev->of_node->parent) {
> 		ret = of_get_phy_mode(mac_np, &interface);
> 		if (ret && ret != -ENODEV) {
> 			of_node_put(mac_np);
> 			of_node_put(phy_node);
> 			return ret;
> 		}
> 		id = of_mdio_parse_addr(ds->dev, phy_node);
> 		if (id == 0)
> 			priv->p5_intf_sel = P5_INTF_SEL_PHY_P0;
> 		if (id == 4)
> 			priv->p5_intf_sel = P5_INTF_SEL_PHY_P4;
> 	}
> 	of_node_put(mac_np);
> 	of_node_put(phy_node);
> 	break;
> }
> 
> if (priv->p5_intf_sel == P5_INTF_SEL_PHY_P0 ||
>     priv->p5_intf_sel == P5_INTF_SEL_PHY_P4)
> 	mt7530_setup_port5(ds, interface);

Smatch doesn't know:
1) What the value of priv->p5_intf_sel is going into this function
2) We enter the for_each_child_of_node() loop
3) That if (phy_node->parent == priv->dev->of_node->parent) { is
   definitely true for one element on the list.

Looking at how Smatch parses this code, I could probably improve problem
#1 a bit.  Right now Smatch sees "struct mt7530_priv *priv = ds->priv;"
and "priv->p5_intf_sel" is unknown, but I could probably improve it to
where it says that it's in the 1-3 range.  But that doesn't help here
and it doesn't address problems 2 and 3.

It's a hard problem.

regards,
dan carpenter