netdev - RE: [net-next 08/13] fsl/fman: check pcsphy pointer before use

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Date:   Wed, 5 Oct 2016 09:08:23 +0000
From:   Madalin-Cristian Bucur <madalin.bucur@....com>
To:     David Laight <David.Laight@...LAB.COM>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "linuxdev.baldrick@...il.com" <linuxdev.baldrick@...il.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [net-next 08/13] fsl/fman: check pcsphy pointer before use

> -----Original Message-----
> From: David Laight [mailto:David.Laight@...LAB.COM]
> Sent: Tuesday, October 04, 2016 5:44 PM
> To: Madalin-Cristian Bucur <madalin.bucur@....com>;
> netdev@...r.kernel.org
> Cc: linuxdev.baldrick@...il.com; linuxppc-dev@...ts.ozlabs.org;
> davem@...emloft.net; linux-kernel@...r.kernel.org
> Subject: RE: [net-next 08/13] fsl/fman: check pcsphy pointer before use
> 
> From: Madalin Bucur
> > Sent: 04 October 2016 08:33
> > Subject: [net-next 08/13] fsl/fman: check pcsphy pointer before use
> ..
> > --- a/drivers/net/ethernet/freescale/fman/fman_memac.c
> > +++ b/drivers/net/ethernet/freescale/fman/fman_memac.c
> > @@ -507,6 +507,9 @@ static void setup_sgmii_internal_phy(struct
> fman_mac *memac,
> >  {
> >  	u16 tmp_reg16;
> >
> > +	if (WARN_ON(!memac->pcsphy))
> > +		return;
> > +
> 
> Why?
> 
> Either it can validly be NULL in which case you don't want the message.
> Or it shouldn't be NULL in which case you need to find and fix the bug.
> The later kernel OOPS will make the bug much easier to find.
> 
> 	David

You can get into that situation if you have a broken device tree, state into
which someone may get while trying to create the device tree for a new
board. Avoiding a crash here allows the user to look at the device trees as
seen by the kernel / add some debug code if needed.

Madalin