linux-kernel - Re: [PATCH] net: stmmac: add explicit check and error on invalid PTP clock rate

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Message-Id: <DA666WVCP2OB.300LVHEGH5V4Y@bootlin.com>
Date: Mon, 26 May 2025 16:42:42 +0200
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: "Yanteng Si" <si.yanteng@...ux.dev>, "Alexandre Torgue"
 <alexandre.torgue@...s.st.com>, "Jose Abreu" <joabreu@...opsys.com>,
 "Andrew Lunn" <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>, "Maxime
 Coquelin" <mcoquelin.stm32@...il.com>, "Richard Cochran"
 <richardcochran@...il.com>
Cc: "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>, "Maxime Chevallier"
 <maxime.chevallier@...tlin.com>, <netdev@...r.kernel.org>,
 <linux-stm32@...md-mailman.stormreply.com>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: stmmac: add explicit check and error on invalid
 PTP clock rate

On Mon May 26, 2025 at 4:22 AM CEST, Yanteng Si wrote:
> 在 5/23/25 7:46 PM, Alexis LothorÃ© 写道:
>> While some platforms implementing dwmac open-code the clk_ptp_rate
>> value, some others dynamically retrieve the value at runtime. If the
>> retrieved value happens to be 0 for any reason, it will eventually
>> propagate up to PTP initialization when bringing up the interface,
>> leading to a divide by 0:

[...]

>  From your description, I cannot determine the scope
> of "some platforms". My point is: if there are only
> a few platforms, can we find a way to handle this in
> the directory of the corresponding platform?

>From what I can see, it can affect any platform using the stmmac driver as
the platform driver (except maybe dwmac-qcom-ethqos.c, which enforces an
open-coded clk_ptp_rate after the stmmac_probe_config_dt call that sets
the clk_ptp_rate), if the platform declares a dedicated clk_ptp_ref clock.
So I would rather say that it can affect most of the platforms.

In my case, I have observed the issue with the dwmac-stm32.c driver, on an
STM32MP157a-dk1 platform.

> And there need a Fixes tag.

Ok, I'll add a relevant Fixes tag.

Alexis

>> Signed-off-by: Alexis Lothoré <alexis.lothore@...tlin.com>
>> ---
>>   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>> 
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> index 918d7f2e8ba992208d7d6521a1e9dba01086058f..f68e3ece919cc88d0bf199a394bc7e44b5dee095 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> @@ -835,6 +835,11 @@ int stmmac_init_tstamp_counter(struct stmmac_priv *priv, u32 systime_flags)
>>   	if (!(priv->dma_cap.time_stamp || priv->dma_cap.atime_stamp))
>>   		return -EOPNOTSUPP;
>>   
>> +	if (!priv->plat->clk_ptp_rate) {
>> +		netdev_err(priv->dev, "Invalid PTP clock rate");
>> +		return -EINVAL;
>> +	}
>> +
>>   	stmmac_config_hw_tstamping(priv, priv->ptpaddr, systime_flags);
>>   	priv->systime_flags = systime_flags;
>>   
>> 
>> ---
>> base-commit: e0e2f78243385e7188a57fcfceb6a19f723f1dff
>> change-id: 20250522-stmmac_tstamp_div-f55112f06029
>> 
>> Best regards,

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com