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Date:   Sat, 4 Apr 2020 17:08:10 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Chuanhong Guo <gch981213@gmail.com>
Cc:     =?iso-8859-1?Q?Ren=E9?= van Dorst <opensource@vdorst.com>,
        netdev@vger.kernel.org, stable@vger.kernel.org,
        Sean Wang <sean.wang@mediatek.com>,
        Vivien Didelot <vivien.didelot@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Russell King <rmk+kernel@armlinux.org.uk>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@lists.infradead.org>,
        linux-mediatek@lists.infradead.org,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] net: dsa: mt7530: fix null pointer dereferencing in
 port5 setup
Message-ID: <20200404150810.GA161768@lunn.ch>
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On Sat, Apr 04, 2020 at 11:19:10AM +0800, Chuanhong Guo wrote:
> Hi!
> 
> On Sat, Apr 4, 2020 at 2:09 AM Ren? van Dorst <opensource@vdorst.com> wrote:
> >
> > Quoting Chuanhong Guo <gch981213@gmail.com>:
> >
> > Hi Chuanhong,
> >
> > > The 2nd gmac of mediatek soc ethernet may not be connected to a PHY
> > > and a phy-handle isn't always available.
> > > Unfortunately, mt7530 dsa driver assumes that the 2nd gmac is always
> > > connected to switch port 5 and setup mt7530 according to phy address
> > > of 2nd gmac node, causing null pointer dereferencing when phy-handle
> > > isn't defined in dts.
> >
> > MT7530 tries to detect if 2nd GMAC is using a phy with phy-address 0 or 4.
> 
> What if the 2nd GMAC connects to an external PHY on address 0 on a
> different mdio-bus?

In general, you using a phy-handle to cover such a situation. If there
is a phy-handle, just use it.

   Andrew