Subject: Re: [PATCH net-next 07/15] net: dsa: mt7530: do not run mt7530_setup_port5() if port 5 is disabled

From: Simon Horman <[email-masked]>
Date: Wed, 6 Dec 2023 21:46:18 +0000

+ Dan Carpenter <[email-masked]>

On Sat, Dec 02, 2023 at 11:45:42AM +0300, Arınç ÜNAL wrote:
> Hi Simon.
> 
> On 21.11.2023 21:53, Simon Horman wrote:
> > On Sat, Nov 18, 2023 at 03:31:57PM +0300, Arınç ÜNAL wrote:
> > > There's no need to run all the code on mt7530_setup_port5() if port 5 is
> > > disabled. The only case for calling mt7530_setup_port5() from
> > > mt7530_setup() is when PHY muxing is enabled. That is because port 5 is not
> > > defined as a port on the devicetree, therefore, it cannot be controlled by
> > > phylink.
> > > 
> > > Because of this, run mt7530_setup_port5() if priv->p5_intf_sel is
> > > P5_INTF_SEL_PHY_P0 or P5_INTF_SEL_PHY_P4. Remove the P5_DISABLED case from
> > > mt7530_setup_port5().
> > > 
> > > Stop initialising the interface variable as the remaining cases will always
> > > call mt7530_setup_port5() with it initialised.
> > > 
> > > Signed-off-by: Arınç ÜNAL <[email-masked]>
> > > Reviewed-by: Vladimir Oltean <[email-masked]>
> > > ---
> > >   drivers/net/dsa/mt7530.c | 9 +++------
> > >   1 file changed, 3 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> > > index fc87ec817672..1aab4c3f28b0 100644
> > > --- a/drivers/net/dsa/mt7530.c
> > > +++ b/drivers/net/dsa/mt7530.c
> > > @@ -942,9 +942,6 @@ static void mt7530_setup_port5(struct dsa_switch *ds, phy_interface_t interface)
> > >   		/* MT7530_P5_MODE_GMAC: P5 -> External phy or 2nd GMAC */
> > >   		val &= ~MHWTRAP_P5_DIS;
> > >   		break;
> > > -	case P5_DISABLED:
> > > -		interface = PHY_INTERFACE_MODE_NA;
> > > -		break;
> > >   	default:
> > >   		dev_err(ds->dev, "Unsupported p5_intf_sel %d\n",
> > >   			priv->p5_intf_sel);
> > > @@ -2313,8 +2310,6 @@ mt7530_setup(struct dsa_switch *ds)
> > >   		 * Set priv->p5_intf_sel to the appropriate value if PHY muxing
> > >   		 * is detected.
> > >   		 */
> > > -		interface = PHY_INTERFACE_MODE_NA;
> > > -
> > >   		for_each_child_of_node(dn, mac_np) {
> > >   			if (!of_device_is_compatible(mac_np,
> > >   						     "mediatek,eth-mac"))
> > > @@ -2346,7 +2341,9 @@ mt7530_setup(struct dsa_switch *ds)
> > >   			break;
> > >   		}
> > > -		mt7530_setup_port5(ds, interface);
> > > +		if (priv->p5_intf_sel == P5_INTF_SEL_PHY_P0 ||
> > > +		    priv->p5_intf_sel == P5_INTF_SEL_PHY_P4)
> > > +			mt7530_setup_port5(ds, interface);
> > 
> > Hi Arınç,
> > 
> > It appears that interface is now uninitialised here.
> > 
> > Flagged by Smatch.
> 
> 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.

Yes, I see your point now. At a guess, perhaps it because:

1. It doesn't know that of_get_phy_mode will set the value of interface
2. It doesn't know if the loop will run (more than zero times)

I CCed Dan Carpenter, who is surely more knowledgeable about this than I,
in case he wants to add anything.

> 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);
> 
> Arınç