linux-kernel - Re: [PATCH net] net: fec: don't save PTP state if PTP is unsupported

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Message-ID: <20241009125214.GV99782@kernel.org>
Date: Wed, 9 Oct 2024 13:52:14 +0100
From: Simon Horman <horms@...nel.org>
To: Wei Fang <wei.fang@....com>
Cc: "davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"richardcochran@...il.com" <richardcochran@...il.com>,
	"csokas.bence@...lan.hu" <csokas.bence@...lan.hu>,
	Shenwei Wang <shenwei.wang@....com>,
	Clark Wang <xiaoning.wang@....com>,
	"linux@...ck-us.net" <linux@...ck-us.net>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: fec: don't save PTP state if PTP is unsupported

On Wed, Oct 09, 2024 at 12:43:50PM +0000, Wei Fang wrote:
> > -----Original Message-----
> > From: Simon Horman <horms@...nel.org>
> > Sent: 2024年10月9日 19:55
> > To: Wei Fang <wei.fang@....com>
> > Cc: davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> > pabeni@...hat.com; richardcochran@...il.com; csokas.bence@...lan.hu;
> > Shenwei Wang <shenwei.wang@....com>; Clark Wang
> > <xiaoning.wang@....com>; linux@...ck-us.net; imx@...ts.linux.dev;
> > netdev@...r.kernel.org; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH net] net: fec: don't save PTP state if PTP is unsupported
> >
> > On Tue, Oct 08, 2024 at 02:11:53PM +0800, Wei Fang wrote:
> > > Some platforms (such as i.MX25 and i.MX27) do not support PTP, so on
> > > these platforms fec_ptp_init() is not called and the related members
> > > in fep are not initialized. However, fec_ptp_save_state() is called
> > > unconditionally, which causes the kernel to panic. Therefore, add a
> > > condition so that fec_ptp_save_state() is not called if PTP is not
> > > supported.
> > >
> > > Fixes: a1477dc87dc4 ("net: fec: Restart PPS after link state change")
> > > Reported-by: Guenter Roeck <linux@...ck-us.net>
> > > Closes:
> > https://lore.ker/
> > nel.org%2Flkml%2F353e41fe-6bb4-4ee9-9980-2da2a9c1c508%40roeck-us.net
> > %2F&data=05%7C02%7Cwei.fang%40nxp.com%7Cb10cac9ed8cd43284aae08
> > dce85930cd%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63864
> > 0716999752935%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLC
> > JQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=1
> > gxwnxNjk91xX7I%2Foco%2F4OhBbxNCryhDMo72O9Jkr2w%3D&reserved=0
> > > Signed-off-by: Wei Fang <wei.fang@....com>
> > > ---
> > >  drivers/net/ethernet/freescale/fec_main.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/freescale/fec_main.c
> > b/drivers/net/ethernet/freescale/fec_main.c
> > > index 60fb54231ead..1b55047c0237 100644
> > > --- a/drivers/net/ethernet/freescale/fec_main.c
> > > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > > @@ -1077,7 +1077,8 @@ fec_restart(struct net_device *ndev)
> > >     u32 rcntl = OPT_FRAME_SIZE | 0x04;
> > >     u32 ecntl = FEC_ECR_ETHEREN;
> > >
> > > -   fec_ptp_save_state(fep);
> > > +   if (fep->bufdesc_ex)
> > > +           fec_ptp_save_state(fep);
> >
> > Hi,
> >
> > I am wondering if you considered adding this check to (the top of)
> > fec_ptp_save_state. It seems like it would both lead to a smaller
> > change and be less error-prone to use.
> >
> 
> Yes, I considered this solution, but when I thought about it,
> fec_ptp_save_state() and fec_ptp_restore_state() are a pair. If
> the check is added to fec_ptp_save_state(), it is better to add
> it to fec_ptp_restore_state(). However, considering that this is
> not related to the current problem, and there are relatively few
> calls to fec_ptp_restore_state(), I did not do this. If there are more
> calls to fec_ptp_restore_state()/fec_ptp_restore_state() in the
> future, I will consider it.

Sure, I agree on your point regarding symmetry, which I had not considered
when I wrote my previous email.  And I agree that the patch is suitable for
net in it's current form.

Reviewed-by: Simon Horman <horms@...nel.org>

...