netdev - RE: [PATCH net 1/2] net: fec_ptp: add clock rate zero check

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Date:   Wed, 16 Jun 2021 11:40:29 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Russell King <linux@...linux.org.uk>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...s.st.com" <alexandre.torgue@...s.st.com>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH net 1/2] net: fec_ptp: add clock rate zero check


Hi Russell,

> -----Original Message-----
> From: Russell King <linux@...linux.org.uk>
> Sent: 2021年6月16日 18:21
> To: Joakim Zhang <qiangqing.zhang@....com>
> Cc: davem@...emloft.net; kuba@...nel.org; peppe.cavallaro@...com;
> alexandre.torgue@...s.st.com; joabreu@...opsys.com;
> mcoquelin.stm32@...il.com; netdev@...r.kernel.org;
> linux-kernel@...r.kernel.org; linux-stm32@...md-mailman.stormreply.com;
> linux-arm-kernel@...ts.infradead.org; dl-linux-imx <linux-imx@....com>
> Subject: Re: [PATCH net 1/2] net: fec_ptp: add clock rate zero check
> 
> On Wed, Jun 16, 2021 at 05:14:25PM +0800, Joakim Zhang wrote:
> > From: Fugang Duan <fugang.duan@....com>
> >
> > Add clock rate zero check to fix coverity issue of "divide by 0".
> >
> > Fixes: commit 85bd1798b24a ("net: fec: fix spin_lock dead lock")
> > Signed-off-by: Fugang Duan <fugang.duan@....com>
> > Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> > ---
> >  drivers/net/ethernet/freescale/fec_ptp.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/freescale/fec_ptp.c
> > b/drivers/net/ethernet/freescale/fec_ptp.c
> > index 1753807cbf97..7326a0612823 100644
> > --- a/drivers/net/ethernet/freescale/fec_ptp.c
> > +++ b/drivers/net/ethernet/freescale/fec_ptp.c
> > @@ -604,6 +604,10 @@ void fec_ptp_init(struct platform_device *pdev, int
> irq_idx)
> >  	fep->ptp_caps.enable = fec_ptp_enable;
> >
> >  	fep->cycle_speed = clk_get_rate(fep->clk_ptp);
> > +	if (!fep->cycle_speed) {
> > +		fep->cycle_speed = NSEC_PER_SEC;
> > +		dev_err(&fep->pdev->dev, "clk_ptp clock rate is zero\n");
> 
> If this is supposed to be an error message, it doesn't convey that something is
> really wrong to the user. Maybe something like this would be more meaningful
> to the user:
> 
> 	"PTP clock rate should not be zero, using 1GHz instead. PTP
> 	clock may be unreliable.\n"
Make Sense.

> It may be appropriate not to publish PTP support for the interface if we don't
> have a valid clock rate, which is probably the safer approach and would
> probably make the problem more noticable to the end user so it gets fixed.

Do you mean that print an error message then return directly? It seems better.

if (!fep->cycle_speed) {
	dev_err(&fep->pdev->dev, "PTP clock rate should not be zero!\n");
	return;
}

Best Regards,
Joakim Zhang
> --
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