On Saturday 05/16 at 13:32 +0200, Michael Byczkowski wrote:

quoted

On 25. Apr 2026, at 19:18, Michael Byczkowski [off-list ref] wrote:

I found three issues in the PPS subsystem that cause unnecessary jitter
under PREEMPT_RT, while being fully backward-compatible with non-RT
kernels:

1. pps-gpio: The IRQ handler is force-threaded on PREEMPT_RT, so the
PPS timestamp is captured after scheduling delay rather than at
interrupt entry. Fix: split into a hardirq primary handler (captures
timestamp only) and a threaded handler (processes the event).

2. pps_device.lock: spinlock_t becomes a sleeping mutex on PREEMPT_RT,
allowing pps_event() to be preempted mid-update. Fix: convert to
raw_spinlock_t and move sleeping calls out of the critical section.

3. pps_kc_hardpps_lock: Same issue as (2), in the kernel consumer path
that calls hardpps(). Fix: convert to DEFINE_RAW_SPINLOCK.

All three patches are tested on a Raspberry Pi 5 running a 7.0.0-rc6
PREEMPT_RT kernel. On non-RT kernels there is zero behavioral change.

Signed-off-by: Michael Byczkowski <redacted>
Acked-by: Rodolfo Giometti <giometti@enneenne.com>
Tested-by: Michael Byczkowski <redacted>

by (3):
pps: pps-gpio: split IRQ handler into hardirq and threaded parts
pps: convert pps_device lock to raw_spinlock for PREEMPT_RT
pps: convert pps_kc_hardpps_lock to raw_spinlock for PREEMPT_RT

drivers/pps/clients/pps-gpio.c | 37 +++++++++++++++++++++++-----------
drivers/pps/kapi.c             | 18 ++++++++++-------
drivers/pps/kc.c               | 22 ++++++++++----------
drivers/pps/pps.c              | 16 +++++++--------
include/linux/pps_kernel.h     |  2 +-
5 files changed, 56 insertions(+), 39 deletions(-)

-- 
2.47.3

Gentle ping on this series. v4 patches 1/3 and 3/3 carried Rodolfo's
Acked-by; v5 addressed the remaining feedback on 2/3. Happy to rework
anything or split the series if that helps it move forward.

Unfortunately apple mail is corrupting your patches :/

Greg KH usually applies patches for drivers/pps/, but I didn't add him
here yet because the patches don't apply.

If you can point me at a git branch for v5, I'd be happy to re-send the
patches myself with your authorship. This is all useful for me and I'd
like to help :)

If you do it yourself, just make sure to add Greg to the Cc: list.

Cheers,
Calvin

Adding linux-rt-users@ and Sebastian on Cc in case there's interest from the
PREEMPT_RT side.