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, consider that any time
set in the past is an offset regarding the MAC system time. This way,
this does not impact existing scripts and the past time use case is
handled. Edit: But maybe that's not important and we can just change
the default behavior to this.

Example to generate a flexible PPS signal that has a 1s period 3s
relative to when the command was entered:

echo "0 3 0 1 1" > /sys/class/ptp/ptp0/period

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
---
Changes in v3:
- Fix warning on braces for the switch case.
- Link to v2: https://lore.kernel.org/r/20250729-relative_flex_pps-v2-0-3e5f03525c45@foss.st.com

Changes in v2:
- Drop STMMAC_RELATIVE_FLEX_PPS config switch
- Add PTP reference clock in stm32mp13x SoCs
- Link to v1: https://lore.kernel.org/r/20250724-relative_flex_pps-v1-0-37ca65773369@foss.st.com

---
Gatien Chevallier (2):
      drivers: net: stmmac: handle start time set in the past for flexible PPS
      ARM: dts: stm32: add missing PTP reference clocks on stm32mp13x SoCs

 arch/arm/boot/dts/st/stm32mp131.dtsi             |  2 ++
 arch/arm/boot/dts/st/stm32mp133.dtsi             |  2 ++
 drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c | 35 +++++++++++++++++++++++-
 3 files changed, 38 insertions(+), 1 deletion(-)
---
base-commit: 242041164339594ca019481d54b4f68a7aaff64e
change-id: 20250723-relative_flex_pps-faa2fbcaf835

Best regards,
-- 
Gatien Chevallier <gatien.chevallier@foss.st.com>