On 2025-05-27 15:36:37 [+0200], Gatien CHEVALLIER wrote:

Hello Sebastian,

Hello Gatien,

Can you elaborate on "This flag change makes not difference on
!PREEMPT_RT" please? IIUC,this makes the callback not run in hard IRQ
context, even in !PREEMPT_RT, no?

If you set
- HRTIMER_MODE_REL_HARD
  then the callback runs in
  - hardirq context on !PREEMPT_RT
  - hardirq context on PREEMPT_RT.

- HRTIMER_MODE_REL
  then the callback runs in
  - hardirq context on !PREEMPT_RT
  - preemptible softirq on PREEMPT_RT.

- HRTIMER_MODE_REL_SOFT
  then the callback runs in
  - softirq context on !PREEMPT_RT
  - preemptible softirq on PREEMPT_RT.

Therefore if you switch HRTIMER_MODE_REL_HARD -> HRTIMER_MODE_REL then
it is a nop on !PREEMPT_RT.

Regarding the need of the spin_lock: gpio_keys_irq_timer() and
gpio_keys_irq_isr() appear to access the same resources. Can't we
have a concurrent access on it from:
HR timer interrupt // GPIO interrupt?

Yes, it could.

But looking back at the patch, this situation does not depend on
the HRTIMER_MODE_REL_HARD flag. So maybe it should be addressed
separately.

Yes, please.

On the other hand, I should use the new
guard(spinlock_irqsave)(&bdata->lock);

Yes, please. The other instance already does so.

Sebastian