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

Hi Russell,

-----Original Message-----
From: Russell King <linux@armlinux.org.uk>
Sent: 2021年6月16日 18:21
To: Joakim Zhang <redacted>
Cc: davem@davemloft.net; kuba@kernel.org; peppe.cavallaro@st.com;
alexandre.torgue@foss.st.com; joabreu@synopsys.com;
mcoquelin.stm32@gmail.com; netdev@vger.kernel.org;
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linux-arm-kernel@lists.infradead.org; dl-linux-imx [off-list ref]
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:

quoted

From: Fugang Duan <redacted>

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 <redacted>
Signed-off-by: Joakim Zhang <redacted>
---
 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)

quoted

 	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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