linux-kernel - Re: [PATCH net-next v3 1/2] drivers: net: stmmac: handle start time set in the past for flexible PPS

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Message-ID: <20250829171548.68d7addd@kernel.org>
Date: Fri, 29 Aug 2025 17:15:48 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Gatien CHEVALLIER <gatien.chevallier@...s.st.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>,
 "Alexandre Torgue" <alexandre.torgue@...s.st.com>, Richard Cochran
 <richardcochran@...il.com>, Rob Herring <robh@...nel.org>, "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 <netdev@...r.kernel.org>, <linux-stm32@...md-mailman.stormreply.com>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
 <devicetree@...r.kernel.org>
Subject: Re: [PATCH net-next v3 1/2] drivers: net: stmmac: handle start time
 set in the past for flexible PPS

On Fri, 29 Aug 2025 12:51:40 +0200 Gatien CHEVALLIER wrote:
> On 8/28/25 04:31, Jakub Kicinski wrote:
> > On Wed, 27 Aug 2025 13:04:58 +0200 Gatien Chevallier wrote:  
> >> +		curr_time = ns_to_timespec64(ns);
> >> +		if (target_ns < ns + PTP_SAFE_TIME_OFFSET_NS) {
> >> +			cfg->start = timespec64_add_safe(cfg->start, curr_time);  
> > 
> > Is there a strong reason to use timespec64_add_safe()?
> > It's not exported to modules:
> > ERROR: modpost: "timespec64_add_safe" [drivers/net/ethernet/stmicro/stmmac/stmmac.ko] undefined!  
> 
> Hello Jakub,
> 
> you're absolutely right. I don't know how I did not encounter the build
> error while performing some tests, that I'm getting now as well.
> 
> The handling of overflows is already done in that function. Either
> I can make a patch to export the symbol or handle the computation in the
> driver. What do you think is best?

The odds of me being right about time related code are only slightly
better than 50/50, and I don't know what "flexible PPS" is :)
But in principle, if the reason you need to check for overflow is valid
-- add the export. The time maintainers will tell us if they don't
want it.