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

[Jakub Kicinski <kuba@kernel.org>]

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?