linux-kernel - Re: [PATCH net-next 0/2] net: stmmac: allow generation of flexible PPS relative to MAC time

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Message-ID: <20250725172547.13d550a4@kernel.org>
Date: Fri, 25 Jul 2025 17:25:47 -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>, <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-next 0/2] net: stmmac: allow generation of flexible
 PPS relative to MAC time

On Thu, 24 Jul 2025 14:31:17 +0200 Gatien Chevallier wrote:
> When doing some testing on stm32mp2x platforms(MACv5), I noticed that
> the command previously used with a MACv4 for genering a PPS signal:
> echo "0 0 0 1 1" > /sys/class/ptp/ptp0/period
> did not work.
> 
> This is because the arguments passed through this command must contain
> the start time at which the PPS should be generated, relative to the
> MAC system time. For some reason, a time set in the past seems to work
> with a MACv4.
> 
> Because passing such an argument is tedious, introduce
> STMMAC_RELATIVE_FLEX_PPS config switch so that the MAC system time
> is added to the args to the stmmac_ptp driver.
> 
> Example to generate a flexible PPS signal that has a 1s period 3s
> relative to when the command was entered before and after setting
> STMMAC_RELATIVE_FLEX_PPS:
> 
> Before: echo "0 175xxxxxxx 0 1 1" > /sys/class/ptp/ptp0/period
> 
> After: echo "0 3 0 1 1" > /sys/class/ptp/ptp0/period

Kconfig doesn't seem like a great way of achieving the outcome.
Some per-platform knob would be better.
But ideally we wouldn't do either. Could we possibly guess which
format user has chosen based on the values, at runtime?