netdev - Re: [PATCH net 2/2] net: stmmac: fix multiplication overflow when reading timestamp

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Message-Id: <D9DAOEKXJKQB.HHD75KOLKIW1@bootlin.com>
Date: Tue, 22 Apr 2025 18:06:18 +0200
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: "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>, "Alexandre Torgue"
 <alexandre.torgue@...s.st.com>, "Richard Cochran"
 <richardcochran@...il.com>, "Daniel Machon" <daniel.machon@...rochip.com>,
 "Maxime Chevallier" <maxime.chevallier@...tlin.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...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 2/2] net: stmmac: fix multiplication overflow when
 reading timestamp

Hello Russell,

On Tue Apr 22, 2025 at 5:32 PM CEST, Russell King (Oracle) wrote:
> On Tue, Apr 22, 2025 at 05:07:23PM +0200, Alexis Lothoré wrote:
>>  	ns = readl(ptpaddr + GMAC_PTP_ATNR);
>> -	ns += readl(ptpaddr + GMAC_PTP_ATSR) * NSEC_PER_SEC;
>> +	ns += (u64)(readl(ptpaddr + GMAC_PTP_ATSR)) * NSEC_PER_SEC;
>
> I'm not sure what the extra parens around readl() are actually trying to
> do. Please drop them if they're not useful.

They are indeed not specifically useful in this case, they will be dropped
in v2.

Thanks,

Alexis

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