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Date: Sat, 2 Dec 2023 09:30:26 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
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>,
	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:
> 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 <arinc.unal@...nc9.com>
> > > Reviewed-by: Vladimir Oltean <olteanv@...il.com>
> > > ---
> > >   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.

It's probably due to the complexities involved in analysing the values
of variables, especially when they're in structures that are passed in.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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